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Tuberculosis in the Horse.
GENERAL ARTICLES.
335
stifle (C), over the quarters to the opposite side, and up inside the thigh CD). Now pull firm, wind twice round the upper fetlock,and give the rope (E) to an assistant to hold. The animal's hind feet are thus thoroughly and firmly secured to his own hind quarters. To secure each fore limb take a piece of light cord about a couple of yards long-a piece of good plough line answers well-double it round the fetlock, and pass the loose ends through the loop so formed; then flex the knee, and pass one cord to the inside and the other to the outside under the forearm, and tie on the upper side of the metacarpal bone, as shown in the illustration. The patient can then be placed in any convenient position as required by circumstances.
TUBERCULOSIS IN THE HORSE.
By
J.
M'FADYEAN, M.B., B.Sc., Royal Veterinary College, Edinburgh.
IN the first number of this Journal (page 51) I placed on record two cases of tuberculosis in the horse. These cases derived a larger measure of interest than would otherwise have belonged to them from the fact that no similar cases had been described in this country, where, so far as veterinary literature seemed to indicate, the belief that the equine species had a complete immunity from natural infection was generally accepted. During the past few months I have had the opportunity to examine the principal organs from another case of equine tuberculosis. The clinical history of this case is given at a subsequent part of this number, and what I have to report concerning it must be regarded as the necessary complement to the facts stated by Mr Campbell, in whose practice it occurred. I say necessary complement, because, in such cases, a microscopical examination is required to place the diagnosis beyond doubt or cavil. The organs specially examined by me were the lymphatic glands, the liver, and the kidneys. Lymphatic Glands. The bronchial, mesenteric, and hepatic lymphatic glands were greatly enlarged. The largest formed tumours about twice as big as the fist of a man. They had a tolerably firm consistence (firmer than a healthy gland), and on section the largest were found to be extensively caseated towards the centre, and partly calcified. The condition of the glands was thus similar to that of the same parts in the cases previously described in this Journal. It may here be remarked that so great was the alteration of some of the glands in size and appearance, that they might readily have been mistaken for true neoplasms, but their position indicated clearly that they were hyperplastic enlargements of the lymphatic glands. After hardening in alcohol, sections were cut from the outer less. degenerated part of one of these enlargements. A microscopic examination of such sections stained with picro-carmine or logwood showed what might be described as a diffuse tubercular structure, in which, amid a basis or groundwork of round cells of a lymphoid character, were a great number of giant cells. Sections were next stained by the method of Ehrlich, which revealed the presence of
GENERAL ARTICLES.
tubercle bacilli in inconceivable numbers. The mode of grouping of the bacilli was identical with that seen in the previous cases. In most cases the bacilli were found in clumps within the cells, and the body of the giant cells seemed to be almost entirely made up of them. The Liver. The portion of liver examined by me gave evidence of considerable enlargement of the organ. It was firmer than normal, and dark blue in colour. Near the portal fissure several nodules as large as a hazel nut were partially imbedded in the liver substance. These were evidently slightly hyperplastic lymphatic glands, but no new growths were observable with the naked eye on cutting into the organ. A microscopical examination of the organ showed advanced amyloid degeneration, and minute discrete round-celled areas of infiltration in the connective tissue of the portal canals, or at the margins of the lobules. The amyloid change was of a very interesting character. In sections stained with methyl. violet it was seen that the walls of the intralobular capillaries were almost uniformly thickened by the amyloid change. So very regular was the distribution of the amyloid material that under a low power of the microscope a section appeared as if the intralobular capillaries had been injected with some rosepink material. The intervening columns of liver cells showed the usual condition of atrophy. The larger vessels of the liver were entirely free from the amyloid change. The areas of round-cell infiltration in the liver were inferentially supposed to be commencing miliary tubercles, and a careful examination of sections stained by Ehrlich's method revealed in some of them the specific bacilli. The Kidneys. These were enormously enlarged. The degree of enlargement may be inferred from the statement that the left kidney weighed exactly 5 lbs (normal weight under 30 ounces). The normal shape of the organ was perfectly preserved, the surface was smooth, and the capsule was neither thickened nor adherent. On section the Malpighian bodies were seen to be very large and prominent, and the veins of the medulla were engorged with blood. A microscopic examination showed the enlargement to be that of chronic venous congestion, without any tubercular formation. While the organs were still in a fresh condition I inoculated two rabbits with material from one of the enlarged glands. Having selected a gland about as large as a hen's egg, I incised it with a sterilised knife, and took a little caseous matter on the point of a small sterilised platinum spatula. This was inserted into a hypodermic pocket on the back of each animal. The inoculation was performed on the 4th of October last, and six weeks afterwards (Nov. 14th) both animals were killed. The autopsy revealed almost identical lesions in the two rabbits, these being as follows: There had formed at the seat of inoculation a crater-like round ulcer about as large as a shilling. The base of the ulcer was thickened, and its surface was dry. On detaching the ulcer with the surrounding skin, the base of the ulcer, viewed from the subcutaneous side, was pale yellow and non-vascular, and it was surrounded by a well-defined hypera:mic ring. On the side of inoculation a lymphatic gland near the elbow was enlarged to the size of a horse bean. On opening the abdomen small tubercles were seen to
GENERAL ARTICLES.
337
be scattered through the liver, spleen, and kidneys, and a considerable number of the same were found in both lungs. A microscopic examination of stained sections showed the presence of tubercle bacilli in the miliary tubercles. I have already referred to the general belief among British veterinarians that cases of tuberculosis in the horse are never met with, and my main purpose in recording the two previous cases was to show the erroneousness of that view. In writing my former communication on this subject, I considered it unnecessary to refer to the differential diagnosis of tuberculosis, assuming that all who might read the article would have sufficient bacteriological knowledge to know that the bacillus tuberculosis possesses staining peculiarities that make it impossible for anyone to mistake it for any other known organism. In taking for granted this amount of knowledge on the part of the profession, I was, apparently, too hasty, for, incredible as it may appear, a veterinary teacher, who if we are not misinformed is the lecturer on Pathology at the institution with which he is connected, has recently stated his belief (I) that it is difficult (and to him evidently impossible) to distinguish between the bacillus of tuberculosis and that of glanders, (2) that the horse has an absolute immunity from tuberculosis, and (3) that the reported cases of tuberculosis in the horse were really cases of glanders. To the first of these assertions I cannot bring myself to reply at length. It could never have been made by anyone with the most elementary theoretical knowledge of veterinary bacteriology. In respect of their mode of grouping in the tissues, in the minute structure of the lesions in which they are found, and in their behaviour towards staining reagents, the specific bacilli of glanders and tuberculosis are so unlike that no pathologist can ever mistake the one for the other. Equally discreditable as regards the lack of knowledge displayed by it, is the statement that the horse cannot contract tuberculosis. Numerous cases of tuberculosis in the horse are recorded in recent continental literature, and it seems almost incredible that a teacher of veterinary pathology should be unaware of the fact that Koch's classical essay on the etiology of tuberculosis l contains a reference to four instances in which he was able to satisfy himself of the presence of the specific bacillus in the organs of horses. The third statement-that the reported cases of equine tuberculosis were really cases of glanders-might be pardonable in anyone but a veterinary practitioner. Noone who has ever seen a case of glanders could, after reading the clinical history of the case of Mr Donald and that of Mr Campbell, believe that these were instances of glanders. At the same time it is perhaps not impossible that before the discovery of Koch's bacillus, true cases of equine tuberculosis may have been regarded as glanderous by those who believed and were taught that the horse had an absolute immunity from tuberculosis. It is not likely that cases of glanders or any other disease will be mistaken for tuberculosis, but it appears very certain that, so long 1 Mittheil. des Kaiser], Gesundheitsamtes ]884. Other references to cases recorded since the discovery of Koch's bacillus are :Csokor, Allgemeine Wiener, medic. Zeitung, 1885. Johne, Sachs Jahresber, 1885. Nocard, Recueil de IIIed. Vet., 1885, 1887, 1888.
2A
GENERAL ARTICLES.
as the error that the horse is immune from tuberculosis is traditionally handed down to veterinary students, actual cases of equine tuberculosis will be overlooked, those who encounter them giving them a mental burial by calling them cases of lymphadenoma. The truth of this is well illustrated by the history of the three cases recorded in this Journal. The specimens (lung, splenic tumours, etc.) from Mr Campbell's first case were sent to the Edinburgh Veterinary College as examples of "lymphadenoma" of the horse, and they were inspected by the examiners of the Royal College of Veterinary Surgeons as well as by the veterinary staff of the College. On all hands it was agreed that the case was one of lymphadenoma, and certainly no one suggested that it might have been tubercular. And why? Clearly because their eyes were shut to the tubercular appearance of the organs, by their previous conviction that the horse cannot contract tuberculosis. For, as will be observed from the report of the meeting of the Royal Scottish Veterinary Society, which appears at a subsequent part of this number, it was agreed, even by some who had seen the previous cases and regarded them as lymphadenomatous, that the organs from Mr Campbell's second case had an obviously tubercular appearance. I do not intend to imply by this that every case in which there is lymphatic hyperplasia in the horse, together with the formation of splenic tumours, is to be at once set down as tubercular. That would be to err as far in the opposite direction. I have more than once had occasion to examine splenic neoplasms in which I could not demonstrate the tubercle bacillus. In a ,case recently examined the spleen was enormously enlarged, and in its substance there were many tumours of various sizes. Other tumours scattered along the course of the splenic artery had evidently originated in lymphatic glands. This spleen was brought to me by a knacker within an hour after its removal from the body, and, with a view to determining the nature of the growths, I inoculated from them tubes of glycerine-agar. These were incubated for a month, but nothing grew in them. A microscopic examination of the tumours showed that they were of a lympho-sarcomatous character. It may here be asked, What is meant by "lymphadenoma" as applied to a disease of the horse? If anyone desirous of obtaining a well-defined notion on this point will consult the best-known British text-books, he will find that the authors in speaking of lymphadenoma exhibit a most irritating vagueness. In some of them there is a gaudy picture of what is termed lymphadenoma of the horse's spleen, but the new growths are generally not described as to either their naked eye or microscopic characters. It is surely a too comprehensive designation which is wide enough to embrace all varieties of tumours found in the spleen or in the lymphatic glands. A very fair notion of the clinical picture of equine tuberculosis is furnished by the description which Mr Donald and Mr Campbell have given of the cases that occurred in their practice. Enlargement of the body lymphatic glands, such as occurred in Mr Campbell's second case, appears to be only exceptionally present. On the other hand, enlargement of the mesenteric or other groups of abdominal lymphatic glands is almost invariably present, and in 5 out of 12 cases encountered by Professor N ocard 1 the enlarged glands were discoverable by rectal 1
Recueil de Med. Vet., 1888, p. 589.
GENERAL ARTICLES.
339
exploration. Progressive emaciation, and in the latter stages polyuria, appear to be almost constant symptoms. I would conclude by saying that it is the duty of every practitioner who desires to make our knowledge regarding lymphadenoma and tuberculosis in the horse more full and accurate than it appears to be at present, to carefully follow out the history of cases exhibiting the clinical features previously referred to. Further, when at the autopsy of such cases he finds lesions similar to those described, he ought not to call the case one of lymphadenoma unless the pos~ibility of its having been tuberculosis has been excluded. This, of course, can only be done by a microscopical examination of sections that have been treated by one or other of the approved methods of demonstrating the tubercle bacillus, and recent events make it very clear that care ought to be taken that the person to whom such examination is entrusted possesses sufficient knowledge to enable him to distinguish the tubercle bacillus from that of glanders.
SOME POINTS IN THE MORBID ANATOMY AND HISTOLOGY OF PLEURO-PNEUMONIA. By G. SIMS
WOODHEAD,
M.D., F.R.C.P.Ed., F.R.S.Ed.,
Superintendent Royal College of Physicians' Laboratory, Edinburgh. (Concluded from fXlge r 33.) WHEN we left the subject of pleuro-pneumonia we were considering some of the changes that are met with in the air vesicles, and we had referred to the two kinds of material found under different conditions in these vesicles. It may be well before leaving this part of the subject to point out that subdivision should not stop here. It has been seen that there is first the active catarrhal proliferation of the alveolar epithelium, such as is met with in numerous comparatively acute processes; and secondly, there is the more chronic condition (figs. 8 and 9, p. I32) which is characteristic of the chronic interstitial forms of inflammation of the lung. A far more commonly recognised form of the alveolar contents in pleuro-pneumonia is the fibrinous exudation so characteristic of ordinary acute pneumonia. The alveolar cast is, in fact, in this case formed of exactly the same elements as are the contents of the lymphatics of the inter-lobular septa. In many cases, as is well known, this fibrinous material undergoes the same changes as when thrown out on an ordinary serous surface. It becomes finely granular, opaque, stains brick red with picro-carmine, and is eventually absorbed. In certain very rare cases there is actual organisation in the fibrinous clot in the air vesicle. This occurs where the epithelial layer has been completely detached, and where in consequence the fibrinous material is in direct contact with the delicate connective tissue of the alveolar wall. Of more common occurrence still, is a peculiar condition in which there is apparently a mucoid or hyaline softening of the fibrin or of the greater part of the alveolar contents. This material has then a homogeneous or glassy appearance, and has frequently become separated from the wall of the air vesicle. At
335
stifle (C), over the quarters to the opposite side, and up inside the thigh CD). Now pull firm, wind twice round the upper fetlock,and give the rope (E) to an assistant to hold. The animal's hind feet are thus thoroughly and firmly secured to his own hind quarters. To secure each fore limb take a piece of light cord about a couple of yards long-a piece of good plough line answers well-double it round the fetlock, and pass the loose ends through the loop so formed; then flex the knee, and pass one cord to the inside and the other to the outside under the forearm, and tie on the upper side of the metacarpal bone, as shown in the illustration. The patient can then be placed in any convenient position as required by circumstances.
TUBERCULOSIS IN THE HORSE.
By
J.
M'FADYEAN, M.B., B.Sc., Royal Veterinary College, Edinburgh.
IN the first number of this Journal (page 51) I placed on record two cases of tuberculosis in the horse. These cases derived a larger measure of interest than would otherwise have belonged to them from the fact that no similar cases had been described in this country, where, so far as veterinary literature seemed to indicate, the belief that the equine species had a complete immunity from natural infection was generally accepted. During the past few months I have had the opportunity to examine the principal organs from another case of equine tuberculosis. The clinical history of this case is given at a subsequent part of this number, and what I have to report concerning it must be regarded as the necessary complement to the facts stated by Mr Campbell, in whose practice it occurred. I say necessary complement, because, in such cases, a microscopical examination is required to place the diagnosis beyond doubt or cavil. The organs specially examined by me were the lymphatic glands, the liver, and the kidneys. Lymphatic Glands. The bronchial, mesenteric, and hepatic lymphatic glands were greatly enlarged. The largest formed tumours about twice as big as the fist of a man. They had a tolerably firm consistence (firmer than a healthy gland), and on section the largest were found to be extensively caseated towards the centre, and partly calcified. The condition of the glands was thus similar to that of the same parts in the cases previously described in this Journal. It may here be remarked that so great was the alteration of some of the glands in size and appearance, that they might readily have been mistaken for true neoplasms, but their position indicated clearly that they were hyperplastic enlargements of the lymphatic glands. After hardening in alcohol, sections were cut from the outer less. degenerated part of one of these enlargements. A microscopic examination of such sections stained with picro-carmine or logwood showed what might be described as a diffuse tubercular structure, in which, amid a basis or groundwork of round cells of a lymphoid character, were a great number of giant cells. Sections were next stained by the method of Ehrlich, which revealed the presence of
GENERAL ARTICLES.
tubercle bacilli in inconceivable numbers. The mode of grouping of the bacilli was identical with that seen in the previous cases. In most cases the bacilli were found in clumps within the cells, and the body of the giant cells seemed to be almost entirely made up of them. The Liver. The portion of liver examined by me gave evidence of considerable enlargement of the organ. It was firmer than normal, and dark blue in colour. Near the portal fissure several nodules as large as a hazel nut were partially imbedded in the liver substance. These were evidently slightly hyperplastic lymphatic glands, but no new growths were observable with the naked eye on cutting into the organ. A microscopical examination of the organ showed advanced amyloid degeneration, and minute discrete round-celled areas of infiltration in the connective tissue of the portal canals, or at the margins of the lobules. The amyloid change was of a very interesting character. In sections stained with methyl. violet it was seen that the walls of the intralobular capillaries were almost uniformly thickened by the amyloid change. So very regular was the distribution of the amyloid material that under a low power of the microscope a section appeared as if the intralobular capillaries had been injected with some rosepink material. The intervening columns of liver cells showed the usual condition of atrophy. The larger vessels of the liver were entirely free from the amyloid change. The areas of round-cell infiltration in the liver were inferentially supposed to be commencing miliary tubercles, and a careful examination of sections stained by Ehrlich's method revealed in some of them the specific bacilli. The Kidneys. These were enormously enlarged. The degree of enlargement may be inferred from the statement that the left kidney weighed exactly 5 lbs (normal weight under 30 ounces). The normal shape of the organ was perfectly preserved, the surface was smooth, and the capsule was neither thickened nor adherent. On section the Malpighian bodies were seen to be very large and prominent, and the veins of the medulla were engorged with blood. A microscopic examination showed the enlargement to be that of chronic venous congestion, without any tubercular formation. While the organs were still in a fresh condition I inoculated two rabbits with material from one of the enlarged glands. Having selected a gland about as large as a hen's egg, I incised it with a sterilised knife, and took a little caseous matter on the point of a small sterilised platinum spatula. This was inserted into a hypodermic pocket on the back of each animal. The inoculation was performed on the 4th of October last, and six weeks afterwards (Nov. 14th) both animals were killed. The autopsy revealed almost identical lesions in the two rabbits, these being as follows: There had formed at the seat of inoculation a crater-like round ulcer about as large as a shilling. The base of the ulcer was thickened, and its surface was dry. On detaching the ulcer with the surrounding skin, the base of the ulcer, viewed from the subcutaneous side, was pale yellow and non-vascular, and it was surrounded by a well-defined hypera:mic ring. On the side of inoculation a lymphatic gland near the elbow was enlarged to the size of a horse bean. On opening the abdomen small tubercles were seen to
GENERAL ARTICLES.
337
be scattered through the liver, spleen, and kidneys, and a considerable number of the same were found in both lungs. A microscopic examination of stained sections showed the presence of tubercle bacilli in the miliary tubercles. I have already referred to the general belief among British veterinarians that cases of tuberculosis in the horse are never met with, and my main purpose in recording the two previous cases was to show the erroneousness of that view. In writing my former communication on this subject, I considered it unnecessary to refer to the differential diagnosis of tuberculosis, assuming that all who might read the article would have sufficient bacteriological knowledge to know that the bacillus tuberculosis possesses staining peculiarities that make it impossible for anyone to mistake it for any other known organism. In taking for granted this amount of knowledge on the part of the profession, I was, apparently, too hasty, for, incredible as it may appear, a veterinary teacher, who if we are not misinformed is the lecturer on Pathology at the institution with which he is connected, has recently stated his belief (I) that it is difficult (and to him evidently impossible) to distinguish between the bacillus of tuberculosis and that of glanders, (2) that the horse has an absolute immunity from tuberculosis, and (3) that the reported cases of tuberculosis in the horse were really cases of glanders. To the first of these assertions I cannot bring myself to reply at length. It could never have been made by anyone with the most elementary theoretical knowledge of veterinary bacteriology. In respect of their mode of grouping in the tissues, in the minute structure of the lesions in which they are found, and in their behaviour towards staining reagents, the specific bacilli of glanders and tuberculosis are so unlike that no pathologist can ever mistake the one for the other. Equally discreditable as regards the lack of knowledge displayed by it, is the statement that the horse cannot contract tuberculosis. Numerous cases of tuberculosis in the horse are recorded in recent continental literature, and it seems almost incredible that a teacher of veterinary pathology should be unaware of the fact that Koch's classical essay on the etiology of tuberculosis l contains a reference to four instances in which he was able to satisfy himself of the presence of the specific bacillus in the organs of horses. The third statement-that the reported cases of equine tuberculosis were really cases of glanders-might be pardonable in anyone but a veterinary practitioner. Noone who has ever seen a case of glanders could, after reading the clinical history of the case of Mr Donald and that of Mr Campbell, believe that these were instances of glanders. At the same time it is perhaps not impossible that before the discovery of Koch's bacillus, true cases of equine tuberculosis may have been regarded as glanderous by those who believed and were taught that the horse had an absolute immunity from tuberculosis. It is not likely that cases of glanders or any other disease will be mistaken for tuberculosis, but it appears very certain that, so long 1 Mittheil. des Kaiser], Gesundheitsamtes ]884. Other references to cases recorded since the discovery of Koch's bacillus are :Csokor, Allgemeine Wiener, medic. Zeitung, 1885. Johne, Sachs Jahresber, 1885. Nocard, Recueil de IIIed. Vet., 1885, 1887, 1888.
2A
GENERAL ARTICLES.
as the error that the horse is immune from tuberculosis is traditionally handed down to veterinary students, actual cases of equine tuberculosis will be overlooked, those who encounter them giving them a mental burial by calling them cases of lymphadenoma. The truth of this is well illustrated by the history of the three cases recorded in this Journal. The specimens (lung, splenic tumours, etc.) from Mr Campbell's first case were sent to the Edinburgh Veterinary College as examples of "lymphadenoma" of the horse, and they were inspected by the examiners of the Royal College of Veterinary Surgeons as well as by the veterinary staff of the College. On all hands it was agreed that the case was one of lymphadenoma, and certainly no one suggested that it might have been tubercular. And why? Clearly because their eyes were shut to the tubercular appearance of the organs, by their previous conviction that the horse cannot contract tuberculosis. For, as will be observed from the report of the meeting of the Royal Scottish Veterinary Society, which appears at a subsequent part of this number, it was agreed, even by some who had seen the previous cases and regarded them as lymphadenomatous, that the organs from Mr Campbell's second case had an obviously tubercular appearance. I do not intend to imply by this that every case in which there is lymphatic hyperplasia in the horse, together with the formation of splenic tumours, is to be at once set down as tubercular. That would be to err as far in the opposite direction. I have more than once had occasion to examine splenic neoplasms in which I could not demonstrate the tubercle bacillus. In a ,case recently examined the spleen was enormously enlarged, and in its substance there were many tumours of various sizes. Other tumours scattered along the course of the splenic artery had evidently originated in lymphatic glands. This spleen was brought to me by a knacker within an hour after its removal from the body, and, with a view to determining the nature of the growths, I inoculated from them tubes of glycerine-agar. These were incubated for a month, but nothing grew in them. A microscopic examination of the tumours showed that they were of a lympho-sarcomatous character. It may here be asked, What is meant by "lymphadenoma" as applied to a disease of the horse? If anyone desirous of obtaining a well-defined notion on this point will consult the best-known British text-books, he will find that the authors in speaking of lymphadenoma exhibit a most irritating vagueness. In some of them there is a gaudy picture of what is termed lymphadenoma of the horse's spleen, but the new growths are generally not described as to either their naked eye or microscopic characters. It is surely a too comprehensive designation which is wide enough to embrace all varieties of tumours found in the spleen or in the lymphatic glands. A very fair notion of the clinical picture of equine tuberculosis is furnished by the description which Mr Donald and Mr Campbell have given of the cases that occurred in their practice. Enlargement of the body lymphatic glands, such as occurred in Mr Campbell's second case, appears to be only exceptionally present. On the other hand, enlargement of the mesenteric or other groups of abdominal lymphatic glands is almost invariably present, and in 5 out of 12 cases encountered by Professor N ocard 1 the enlarged glands were discoverable by rectal 1
Recueil de Med. Vet., 1888, p. 589.
GENERAL ARTICLES.
339
exploration. Progressive emaciation, and in the latter stages polyuria, appear to be almost constant symptoms. I would conclude by saying that it is the duty of every practitioner who desires to make our knowledge regarding lymphadenoma and tuberculosis in the horse more full and accurate than it appears to be at present, to carefully follow out the history of cases exhibiting the clinical features previously referred to. Further, when at the autopsy of such cases he finds lesions similar to those described, he ought not to call the case one of lymphadenoma unless the pos~ibility of its having been tuberculosis has been excluded. This, of course, can only be done by a microscopical examination of sections that have been treated by one or other of the approved methods of demonstrating the tubercle bacillus, and recent events make it very clear that care ought to be taken that the person to whom such examination is entrusted possesses sufficient knowledge to enable him to distinguish the tubercle bacillus from that of glanders.
SOME POINTS IN THE MORBID ANATOMY AND HISTOLOGY OF PLEURO-PNEUMONIA. By G. SIMS
WOODHEAD,
M.D., F.R.C.P.Ed., F.R.S.Ed.,
Superintendent Royal College of Physicians' Laboratory, Edinburgh. (Concluded from fXlge r 33.) WHEN we left the subject of pleuro-pneumonia we were considering some of the changes that are met with in the air vesicles, and we had referred to the two kinds of material found under different conditions in these vesicles. It may be well before leaving this part of the subject to point out that subdivision should not stop here. It has been seen that there is first the active catarrhal proliferation of the alveolar epithelium, such as is met with in numerous comparatively acute processes; and secondly, there is the more chronic condition (figs. 8 and 9, p. I32) which is characteristic of the chronic interstitial forms of inflammation of the lung. A far more commonly recognised form of the alveolar contents in pleuro-pneumonia is the fibrinous exudation so characteristic of ordinary acute pneumonia. The alveolar cast is, in fact, in this case formed of exactly the same elements as are the contents of the lymphatics of the inter-lobular septa. In many cases, as is well known, this fibrinous material undergoes the same changes as when thrown out on an ordinary serous surface. It becomes finely granular, opaque, stains brick red with picro-carmine, and is eventually absorbed. In certain very rare cases there is actual organisation in the fibrinous clot in the air vesicle. This occurs where the epithelial layer has been completely detached, and where in consequence the fibrinous material is in direct contact with the delicate connective tissue of the alveolar wall. Of more common occurrence still, is a peculiar condition in which there is apparently a mucoid or hyaline softening of the fibrin or of the greater part of the alveolar contents. This material has then a homogeneous or glassy appearance, and has frequently become separated from the wall of the air vesicle. At