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The Bacteriological Examination of Water Supplies
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Reviews
THE BACTERIOLOGICAL EXAMINATION OF W A T E R
377 SUPPLIES.
By Dr.
W. G. Savage, M.O.H. and Public Analyst, Colchester ; late Lecturer on Bacteriology, University College, Cardiff, &c. Pp. xvi + 297 ; p. 8vo. London : H. K. Lewis. 6s. 6d. nett. This work fully~ustifies the author's description of it as " a book dealing, not merely with the details of practical procedure, but also with the data upon which these methods are based, and the deductions held to be justifiable from them." After a chapter relating to the self-purification of water and the significance of various broad classes of water bacteria, the quantitative bacterial content of natural waters is dealt with. The author condemns the old unsatisfactory numerical standards and assigns a secondary place to enumeration methods. He strongly emphasizes the necessity for uniformity of procedure in water counts and indicates the influence of bacteriological technique on the results obtained. The B. typhosus inevitably comes under discussion, and much evidence of a somewhat contradictory nature is adduced bearing on its viability in soil, sewage, and water. In this connection the author regards the evidence as to its loss of characteristics by saprophytic conditions as weak and unconvincing. Doubt as to the identity of organisms isolated from suspected waters at an earlier bacteriological period lessens the already small list of positive findings in waters suspected of disseminating enteric fever: The practical hopelessness of attempting to isolate from such a source the specific cause of this, the outstanding water-borne disease of this country affords justification to the large proportion of this volume which is occupied by a consideration of bacterial indicators of excretal pollution, and especially the Bacillus coli. Dr. Savage leads up to a detailed consideration of such indicators through successive chapters devoted to the bacteriology of excreta (animal and human), sewage and sewage effluents, and of soil, from which the bacteria found in water are mainly derived. The variability of the characteristics of the coli group and the distribution of the bacillus in Nature are gone into with much detail, a n d the author is strongly of opinion that " there is no evidence or observations which have ever shown that B. coli, reasonably defined, is present in any numbers in sources which have not been exposed to some form of f~ecal contamination." Looking at this organism from the standpoint of " t h e perfect bacterial indicator," the author regards it as a reliable indicator of excretal pollution not necessarily human, its value depending on the completeness of its attributes and its numerical presence. Owing to the wide distribution of animals, "small numbers of the organism do not warrant the condemnation of a water, while large numbers can hardly be due to other than recent and objectionable pollution." I t does not, however, indicate the source of the pollution, which may also be no longer dangerous, and difficulty arises from bacilli which deviate from the characters ascribed to a true Bacillus coli communis. Among other organisms the streptococcus group and the B. enteritidis sporogenes receive attention, and, though important, are regarded as of less value than the B. coli. In a valuable chapter on the interpretation of results Dr. Savage indicates rough standards for widely differing types of water. Chapters follow on the collection and transmission of samples and on laboratory methods of dealing with them, much very useful detail being conveyed. An extensive bibliography is appended.
378
Reviews
[Public Health
Throughout this work there is evidence of its author's complete familiarity with his subject, both from his extensive personal experience and his acquaintance with the work of others. I t contains much original work, and the evidence from all sources is regarded in a fair-minded and truly scientific spirit. We can most strongly recommend it to all who are interested in the subject.
RECENT PROGRESS IN
THE STUDY OF VARIATION, HEREDITY, AND
EVOLUTION. By R. H. Lock, M.A. Murray, 1906, pp. 299; size 8u × 5". Price 7s. 6d. net. Those who have read Mr. Whetham's fascinating volume on The Recent Development o] Physical Science will find a worthy companion volume in Mr. Lock's book. I t is a long time since we read a book which so admirably combines popular treatment and exposition with scientific accuracy and lucidity. The first chapter gives an interesting sketch of biology, the second of evolution, and in the third the theory of natural selection is treated. Next follow chapters on biometry, the theory of mutation, the older hybridists, Mendelism, recent cytology, and a final chapter reviewing the whole subject. Each chapter contains matter which must be novel to all those who have not had the opportunity of keeping their biological reading up to date. In every chapter shrewd criticisms and warnings as to commonly accepted views occur. Thus, it is commonly accepted that Weismann's views have upset the possibility of the inheritance of acquired powers; but instances are given showing that judgment must still be suspended in certain instances. The chapter on biometry, or the statistical study of variations, is a most judicious as well as lucid exposition of a difficult subject ; and we are warned of the elementary fact which there is always a natural tendency to overlook, that " a f t e r even the most elaborate mathematical analysis, the final result cannot be clothed with any greater amount of certainty than the facts from which the calculator sets out." Similarly it is shown that much of the work of the Karl Pearson school on heredity depends on the law of ancestral heredity, which in its original form supposed that every ancestor of a particular individual contributes its quota to the heritable qualities displayed by that individual. This hypothesis Rendel has disproved in specific instances. The account of Professor Johannsen's investigations o n " pure lines" is most interesting. They show that the personal character of a particular ancestor has no influence upon his descendants; only the type to which he belongs influencing the offspring. The chapters on Mendelism are the most valuable in the whole book. I t appears not improbable that Mendel's discovery, made about the year 1865, will be of " an importance little inferior to those of a Newton or a Dalton." His facts introduce the idea of unit characters, capable of being inherited independently of one another. They completely change our ideas of heredity. We no longer look upon the individual as a unit, but as a living mosaic. This law introduces us practically to the possibility of breeding new and useful types of animals and plants. In wheat, for instance, resistance to attacks of disease, good milling quality, lateness of ripening, may all be produced by Mendelian selection; and it is now possible " to take a different example of these qualities from each of three
Reviews
THE BACTERIOLOGICAL EXAMINATION OF W A T E R
377 SUPPLIES.
By Dr.
W. G. Savage, M.O.H. and Public Analyst, Colchester ; late Lecturer on Bacteriology, University College, Cardiff, &c. Pp. xvi + 297 ; p. 8vo. London : H. K. Lewis. 6s. 6d. nett. This work fully~ustifies the author's description of it as " a book dealing, not merely with the details of practical procedure, but also with the data upon which these methods are based, and the deductions held to be justifiable from them." After a chapter relating to the self-purification of water and the significance of various broad classes of water bacteria, the quantitative bacterial content of natural waters is dealt with. The author condemns the old unsatisfactory numerical standards and assigns a secondary place to enumeration methods. He strongly emphasizes the necessity for uniformity of procedure in water counts and indicates the influence of bacteriological technique on the results obtained. The B. typhosus inevitably comes under discussion, and much evidence of a somewhat contradictory nature is adduced bearing on its viability in soil, sewage, and water. In this connection the author regards the evidence as to its loss of characteristics by saprophytic conditions as weak and unconvincing. Doubt as to the identity of organisms isolated from suspected waters at an earlier bacteriological period lessens the already small list of positive findings in waters suspected of disseminating enteric fever: The practical hopelessness of attempting to isolate from such a source the specific cause of this, the outstanding water-borne disease of this country affords justification to the large proportion of this volume which is occupied by a consideration of bacterial indicators of excretal pollution, and especially the Bacillus coli. Dr. Savage leads up to a detailed consideration of such indicators through successive chapters devoted to the bacteriology of excreta (animal and human), sewage and sewage effluents, and of soil, from which the bacteria found in water are mainly derived. The variability of the characteristics of the coli group and the distribution of the bacillus in Nature are gone into with much detail, a n d the author is strongly of opinion that " there is no evidence or observations which have ever shown that B. coli, reasonably defined, is present in any numbers in sources which have not been exposed to some form of f~ecal contamination." Looking at this organism from the standpoint of " t h e perfect bacterial indicator," the author regards it as a reliable indicator of excretal pollution not necessarily human, its value depending on the completeness of its attributes and its numerical presence. Owing to the wide distribution of animals, "small numbers of the organism do not warrant the condemnation of a water, while large numbers can hardly be due to other than recent and objectionable pollution." I t does not, however, indicate the source of the pollution, which may also be no longer dangerous, and difficulty arises from bacilli which deviate from the characters ascribed to a true Bacillus coli communis. Among other organisms the streptococcus group and the B. enteritidis sporogenes receive attention, and, though important, are regarded as of less value than the B. coli. In a valuable chapter on the interpretation of results Dr. Savage indicates rough standards for widely differing types of water. Chapters follow on the collection and transmission of samples and on laboratory methods of dealing with them, much very useful detail being conveyed. An extensive bibliography is appended.
378
Reviews
[Public Health
Throughout this work there is evidence of its author's complete familiarity with his subject, both from his extensive personal experience and his acquaintance with the work of others. I t contains much original work, and the evidence from all sources is regarded in a fair-minded and truly scientific spirit. We can most strongly recommend it to all who are interested in the subject.
RECENT PROGRESS IN
THE STUDY OF VARIATION, HEREDITY, AND
EVOLUTION. By R. H. Lock, M.A. Murray, 1906, pp. 299; size 8u × 5". Price 7s. 6d. net. Those who have read Mr. Whetham's fascinating volume on The Recent Development o] Physical Science will find a worthy companion volume in Mr. Lock's book. I t is a long time since we read a book which so admirably combines popular treatment and exposition with scientific accuracy and lucidity. The first chapter gives an interesting sketch of biology, the second of evolution, and in the third the theory of natural selection is treated. Next follow chapters on biometry, the theory of mutation, the older hybridists, Mendelism, recent cytology, and a final chapter reviewing the whole subject. Each chapter contains matter which must be novel to all those who have not had the opportunity of keeping their biological reading up to date. In every chapter shrewd criticisms and warnings as to commonly accepted views occur. Thus, it is commonly accepted that Weismann's views have upset the possibility of the inheritance of acquired powers; but instances are given showing that judgment must still be suspended in certain instances. The chapter on biometry, or the statistical study of variations, is a most judicious as well as lucid exposition of a difficult subject ; and we are warned of the elementary fact which there is always a natural tendency to overlook, that " a f t e r even the most elaborate mathematical analysis, the final result cannot be clothed with any greater amount of certainty than the facts from which the calculator sets out." Similarly it is shown that much of the work of the Karl Pearson school on heredity depends on the law of ancestral heredity, which in its original form supposed that every ancestor of a particular individual contributes its quota to the heritable qualities displayed by that individual. This hypothesis Rendel has disproved in specific instances. The account of Professor Johannsen's investigations o n " pure lines" is most interesting. They show that the personal character of a particular ancestor has no influence upon his descendants; only the type to which he belongs influencing the offspring. The chapters on Mendelism are the most valuable in the whole book. I t appears not improbable that Mendel's discovery, made about the year 1865, will be of " an importance little inferior to those of a Newton or a Dalton." His facts introduce the idea of unit characters, capable of being inherited independently of one another. They completely change our ideas of heredity. We no longer look upon the individual as a unit, but as a living mosaic. This law introduces us practically to the possibility of breeding new and useful types of animals and plants. In wheat, for instance, resistance to attacks of disease, good milling quality, lateness of ripening, may all be produced by Mendelian selection; and it is now possible " to take a different example of these qualities from each of three