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LIGNOCAINE HYPERSENSITIVITY
1245
POPEYE’S INFLUENCE OVERSEAS ?
Sn;,—The witty and knowledgeable comment by Dr. Richard Hunter (April 10, p. 746) entitled Why Popeye Took Spinach has wider significance in world nutrition, especially for mothers and children in less developed regions. Basically, most of the world’s population are obligatory vegetarians, and, as far as the infant is concerned, breastmilk is often the only food taken, which by itself will supply the full range of essential aminoacids. Apart from this, protein derived from animal sources plays only a small part in infant feeding in most communities, and the transitional weaning diet is of necessity based on food mixtures of vegetable origin. In fact, protein consumed by most of the world comes from cereal staples, such as rice, wheat, and maize. However, the protein quality is deficient in cereals and also lacking in a variety of vitamins and minerals. A logical approach to home-prepared infant weaning foods can, therefore, be made by the " principle of multimixes 1-that is, by combining lysine-deficient cereal with methionine-deficient legume, to which can be added small quantities of various different dark-green leafy vegetables (D.G.L.V.) as rich sources of iron, betacarotene, calcium, &c., as well as folic acid. Variations of this simple-seeming approach are the basis of most village-level triple mixes ", so that the question of the status, cultural image, and modern knowledge of the nutritional value of spinach can have an influence on the question of the use of a range of D.G.L.V. in the diet of young children, pregnant and lactating women, and, indeed, whole communities in less developed, largely tropical regions. The world-wide range of edible D.G.L.V. is very large, including various species of amaranthus and other tropical spinaches, and the leaves of pumpkin, sweet potato, In fact, a search of traditional food patterns cassava, &c. shows that D.G.L.v. are consumed, frequently usually collected wild or semicultivated in casual home gardens. "
"
This
was
the
in Britain until recent decades-for " nettle, and " Good King Henry (Cheno-
case
example, sorrel, podium bonus-henricus). The importance of D.G.L.V. in infant feeding in most developing countries can be considerable, and it is therefore unfortunate to note the apparent decline in their use in many areas of the world and also the relative lack of often given to these foods by nutritionists. for the decreasing emphasis on D.G.L.v. are various. Firstly, there is a world-wide trend away from the ho-.ne-grown towards the purchased. Even in many tropical areas the home garden is regarded as oldfashioned, with country-bumpkin, peasant overtones, while the " cult of the can " has become statusful. The blandishments and persuasion of more-or-less irresponsible hucksters of expensive vitamin preparations, misleadingly labelled tonics, and culturally and economically irrelevant infant foods have too often tended to be the doubtful blessings of the technology and marketing enterprise of the food industry. As part of the same trend, in many areas of the world the fruits and vegetables of prestige and status are those that are imported. This can lead to decreasing emphasis on production of local items, while the imports are always expensive and very often nutritionally much less valuable than more easily available indigenous foods. For example, in some tropical countries the imported apple has status and the local papaya is underused " poor man’s food ". Similarly, D.G.L.V. are outclassed in the status-rating when compared with sometimes imported, anasmic " light-green leafy vegetables of much less nutritional value, such as lettuce and cabbage. Despite ethnic and nationalistic emphasis on traditional
emphasis
The
reasons
"
1.
Jelliffe, D. B. J.
trop. Pediat.
1967, 13, 46.
items of the diet in some places-as, for example, with " soul food " among black Americans-the pattern for modern living, including infant feeding, still tends to strive towards that of industrialised countries in Western Europe and North America. It is therefore of great interest to follow Dr. Hunter’s account of the varied fortunes and vicissitude of spinach, the best known European D.G.L.v. It is apparent that spinach has had a very fluctuant reputation and image in the past two or three decades, moving from mystic " tonic " food to a depressing watery mass to be eaten as punishment, to an over-emphasis on illeffects from nitrates and oxalates. Dr. Hunter’s comment on folic acid’s relation to brainamine metabolism may perhaps add much-needed modern scientific glamour to such rather prosaic-seeming items as spinach and other D.G.L.v. This would, indeed, be most timely since, without in any way being cultist (" the beans and greens school of tropical nutrition "). I believe the significance of D.G.L.V. in many traditional diet patterns has been underappreciated by many nutritionists. In fact, in many communities they can be correctly considered as village-level vitamin and mineral supplements. In addition, their protein content is not negligible, especially dried leaves, with, what is more, an aminoacid range which is complementary to that of cereal staples. Nutritionally it is indeed unfortunate that the Popeye saga is no longer with us. However, with the present nostalgic, escapist trend towards the diversions of a few decades back, it may well be that these cartoons will be revived. If so, they would seem to have built-in nutrition education, not only in relation to D.G.L.v. for feeding infants and mothers in less developed countries, but also possibly in relation to Olive Oyl (low-cholesterol diet) and even to Wimpy (with the hamburger epitomising a logical animal-protein/cereal " double-mix " extender of expensive meat and as a cultural disguiser of otherwise less acceptable bits of beef muscle). Caribbean Food and Nutrition Institute, P.O. Box 140, Kingston, Jamaica.
D. B.
JELLIFFE.
LIGNOCAINE HYPERSENSITIVITY SIR,-Correspondents have questioned the safety of nasal testing for hypersensitivity as advocated by Dr. Eyre and Dr. Nally (Feb. 6, p. 264). I should, however, like to correct the impression given by Eyre and Nally that lignocaine hypersensitivity is exceptionally rare. Dr. McAllen and her colleagues (May 15, p. 1024) have cited reports of a number of patients,- and I am aware of 7 more reported cases.1-4 I should like to emphasise two of the many valuable points raised by Dr. McAllen and her colleagues-that in-vivo testing may be negative although the patient is hypersensitive to a drug, and that the safest methods of investigation are in-vitro tests. I have been using, during the past 18 months, the lymphocyte-transformation technique 5,6 for testing 9 patients referred to me with a possible hypersensitivity to lignocaine after dental treatment. The lymphocyte response, estimated by the uptake of 14C-thymidine, in 4 patients yielded a significant reaction to lignocaine but not to procaine or prilocaine. Intradermal skin-tests applied in 7 patients did not show a positive reaction to any of the 3 local anaesthetics. I hesitate to draw any firm conclusions from these preliminary findings of a small series, but it seems that (a) 1. 2. 3. 4. 5. 6.
Halpern, B., Ky, N. T., Amache, N. J. Allergy, 1967, 40, 168. Holti, G., Hood, F. J. C. Dent. Practit. 1965, 15, 294. Tillman, H. H. Oral Surg. 1958, 11, 1372. Walker, R. T. Br. dent. J. 1971, 130, 2. Nowell, P. C. Cancer Res. 1960, 20, 462. Lehner, T. Immunology, 1967, 13, 159.
1246
lymphocyte-transformation tests can be positive in the absence of a skin-test reaction, as has been reported previously 1; (b) there are no attendant dangers to the patient by using an in-vitro technique; (c) subsequent use of prilocaine for local anxsthesia in 3 of the patients positive to lignocaine were free of any side-effects; (d) hypersensitivity to a variety of drugs can be incorrectly attributed to local anaathetics, particularly during dental treatment when a variety of topical agents and metallic
alloys
are
used.
Department of Oral Immunology and Microbiology, Guy’s Hospital, London SE1 9RT.
THOMAS LEHNER.
PRESENTATION OF ACID-BASE INFORMATION
SIR,-Dr. Flenley (May 8, p. 961) has produced an excellent graph and article on the method of presentation of acid-base information. His derivation of the " confidence limits of the acid-base variables from the world literature is particularly valuable, whatever form of presentation is considered the most useful and desirable. However, I remain unconvinced that the graph of hydrogen-ion activity [H+] versus carbon-dioxide tension (PC02) is any better than other more familiar graphs. Although this graph will be unfamiliar to many, it should be used if it aids understanding and allows a more uniform system for the teaching and presentation of acid-base data. I have three reasons for suggesting that the [H+] - PCÛ2 plot does not justify such a change from more frequently used "
plots. i.
The acid-base variable most often measured on patients in the wards is the total plasma-carbon-dioxide content ([COZ]), sometimes inaccurately called the bicarbonate concentration ([HC03 ]), which is measured routinely with the electrolytes and the urea. It is the variable with which clinician and student are most familiar. For a full and reliable acid-base assessment one obviously needs a measurement of two of the three variables, pH, PC02’ and [C02] on arterial blood. However, by combining the clinical information about the patient with the [C02] in venous blood one can usually decide which is the primary acid-base disturbance and make an approximate estimate of its severity. Further, if one has a few complete acid-base measurements on arterial blood one can use the more frequent daily measurement of [C02] (done with the urea and electrolytes) to assess the progress of the patient. This is especially important when complete acid-base measurements are not frequently or readily available. Enough has been said to demonstrate the dominant role of [CO2] in everyday practice and to suggest that any acid-base plot should include [C02] or bicarbonate. The inclusion of [C02] or bicarbonate as isobars in Dr. Flenley’s proposed diagram would make it a mass of confusing lines and negate its value.
My other objections fundamental:
are
less
important but
no
less
ii. Dr. Flenley mentions the difference between the in-vivo and in-vitro CO2 dissociation curves. To explain this difference to the student it is necessary to show how loss or gain of bicarbonate from the extracellular fluid can affect the relationship between [COz] (or bicarbonate) and Pco2; it is necessary, therefore, to use the CO2 dissociation curve. If one adopts the acid-base diagram suggested by Dr. Flenley as standard, the difference between the in-vivo and in-vitro curves will need to be explained in terms of [H+]. iii. For teaching purposes, at least, it would seem desirable to use the acid-base variables which can be measured. The Pco2 can be measured and is a reliable guide to the level of alveolar ventilation. The [CO2] can be measured and, with the PC02’ can give a clear picture of the acid-base status of the patient. The hydrogen-ion activity or concentration in biological fluids is unknown and not measurable by present-day techniques, although one hopes that glass-
electrode
measurements are some
function of hydrogen-ion
activity. From what I have said it is clear that I favour the
Pco2-[C02] plot for teaching purposes. Its disadvantage is that it is not linear, but this presents no real problem in teaching and in day-to-day clinical use. However, there are many who use the glass electrode in acid-base measurements for technological convenience as with the Astrup technique. For them it is plainly desirable to have a plot in which the numbers read off the pH meter can be directly inserted on the graph. I can see no reason to change from the well known and well tried ph-log Pcoz plot. It is true that when PC02 is zero the ordinate of this graph is discontinuous, being negatively infinite, but I suspect this only disturbs the sleep of the mathematical pedant. I don’t know which is the best graph to use since they all have some disadvantage, be it physiological, chemical, technological, mathematical, or psychological. It is likely that no one plot will meet all needs, and I cannot see any particular advantage of a [H+]-Pco2 plot over a pH[HC03], pH-log PC02’ or even Pco2-[C021 plot. Department of Medicine, Middlesex Hospital, London W1N 8AA.
S.
J. G. SEMPLE.
HOME HEATING AND CHRONIC BRONCHITIS
SIR,-Dr. Segall (May 22, p. 1069) states the case for adequate home heating in the prevention and the treat. ment of bronchitis, but does not discuss (1) desirable temperature levels or (2) relative humidity. Environmental warmth is, within rather wide limits, a matter of habit, and nowadays also of fashion and even of snobbery. While these last factors lead, decade by decade, to ever hotter homes, it does not necessarily follow that this " up-with-the-Jones’ " type of " our house is really properly warm " (enervatingly hot in fact) fashion is producing an atmosphere optimal for health. I suggest that in living accommodation it is unnecessary to go beyond the 62-66°F (16-6-19°C) range, and it is frankly undesirable to go beyond 70 °F (21 °C), and bedrooms should be much cooler. Relative humidity (R.H.) commonly sinks to very low levels in centrally heated premises-e.g., outdoor air at 40 °F (5°C) at 80% relative humidity, when warmed to 70°F (21 °C), yields R.H. of only 26%. Not only in Britain, but in all except very arid and very inland continental areas, the ordinary atmospheric R.H. is much higher than is generally realised. In Britain it is seldom below 60%, usually above 70%, and often exceeds 80%.1 A typical inland site, such as Munich, has average annual values at 0700 hours of 87% R.H., and at 1400 hours of 65 % R.H.2 Low values, almost down to those found in centrally heated premises, obtain in some very hot dry places-e.g. Phoenix, Arizona, with average annual R.H. at 0530 hours of 57% and at 1730 hours of 28%,3 but not everyone would consider these climates to be optimally comfortable. Low R.H. causes high evaporative water loss and drying of respiratory passages, with consequent inspissation of secretions. It is therefore important to humidify the atmosphere for people with respiratory-tract disease.4But why wait for disease ?The minimal desirable Averages of Humidity for the British Isles. Meteorological Officc no. 421. H.M. Stationery Office, 1938. 2. Tables of Temperature, Relative Humidity and Precipitation for the World. Meteorological Office no. 617; part III. H.M. Stationery Office, 1967. 3. Tables of Temperature, Relative Humidity and Precipitation for the World. Meteorological Office no. 617; part I. H.M. Stationery Office, 1958. 4. Walker, J. E. C., Wells, R. E., Merrill, E. W. Am. J. Med. 1961, 30, 259. 1.
POPEYE’S INFLUENCE OVERSEAS ?
Sn;,—The witty and knowledgeable comment by Dr. Richard Hunter (April 10, p. 746) entitled Why Popeye Took Spinach has wider significance in world nutrition, especially for mothers and children in less developed regions. Basically, most of the world’s population are obligatory vegetarians, and, as far as the infant is concerned, breastmilk is often the only food taken, which by itself will supply the full range of essential aminoacids. Apart from this, protein derived from animal sources plays only a small part in infant feeding in most communities, and the transitional weaning diet is of necessity based on food mixtures of vegetable origin. In fact, protein consumed by most of the world comes from cereal staples, such as rice, wheat, and maize. However, the protein quality is deficient in cereals and also lacking in a variety of vitamins and minerals. A logical approach to home-prepared infant weaning foods can, therefore, be made by the " principle of multimixes 1-that is, by combining lysine-deficient cereal with methionine-deficient legume, to which can be added small quantities of various different dark-green leafy vegetables (D.G.L.V.) as rich sources of iron, betacarotene, calcium, &c., as well as folic acid. Variations of this simple-seeming approach are the basis of most village-level triple mixes ", so that the question of the status, cultural image, and modern knowledge of the nutritional value of spinach can have an influence on the question of the use of a range of D.G.L.V. in the diet of young children, pregnant and lactating women, and, indeed, whole communities in less developed, largely tropical regions. The world-wide range of edible D.G.L.V. is very large, including various species of amaranthus and other tropical spinaches, and the leaves of pumpkin, sweet potato, In fact, a search of traditional food patterns cassava, &c. shows that D.G.L.v. are consumed, frequently usually collected wild or semicultivated in casual home gardens. "
"
This
was
the
in Britain until recent decades-for " nettle, and " Good King Henry (Cheno-
case
example, sorrel, podium bonus-henricus). The importance of D.G.L.V. in infant feeding in most developing countries can be considerable, and it is therefore unfortunate to note the apparent decline in their use in many areas of the world and also the relative lack of often given to these foods by nutritionists. for the decreasing emphasis on D.G.L.v. are various. Firstly, there is a world-wide trend away from the ho-.ne-grown towards the purchased. Even in many tropical areas the home garden is regarded as oldfashioned, with country-bumpkin, peasant overtones, while the " cult of the can " has become statusful. The blandishments and persuasion of more-or-less irresponsible hucksters of expensive vitamin preparations, misleadingly labelled tonics, and culturally and economically irrelevant infant foods have too often tended to be the doubtful blessings of the technology and marketing enterprise of the food industry. As part of the same trend, in many areas of the world the fruits and vegetables of prestige and status are those that are imported. This can lead to decreasing emphasis on production of local items, while the imports are always expensive and very often nutritionally much less valuable than more easily available indigenous foods. For example, in some tropical countries the imported apple has status and the local papaya is underused " poor man’s food ". Similarly, D.G.L.V. are outclassed in the status-rating when compared with sometimes imported, anasmic " light-green leafy vegetables of much less nutritional value, such as lettuce and cabbage. Despite ethnic and nationalistic emphasis on traditional
emphasis
The
reasons
"
1.
Jelliffe, D. B. J.
trop. Pediat.
1967, 13, 46.
items of the diet in some places-as, for example, with " soul food " among black Americans-the pattern for modern living, including infant feeding, still tends to strive towards that of industrialised countries in Western Europe and North America. It is therefore of great interest to follow Dr. Hunter’s account of the varied fortunes and vicissitude of spinach, the best known European D.G.L.v. It is apparent that spinach has had a very fluctuant reputation and image in the past two or three decades, moving from mystic " tonic " food to a depressing watery mass to be eaten as punishment, to an over-emphasis on illeffects from nitrates and oxalates. Dr. Hunter’s comment on folic acid’s relation to brainamine metabolism may perhaps add much-needed modern scientific glamour to such rather prosaic-seeming items as spinach and other D.G.L.v. This would, indeed, be most timely since, without in any way being cultist (" the beans and greens school of tropical nutrition "). I believe the significance of D.G.L.V. in many traditional diet patterns has been underappreciated by many nutritionists. In fact, in many communities they can be correctly considered as village-level vitamin and mineral supplements. In addition, their protein content is not negligible, especially dried leaves, with, what is more, an aminoacid range which is complementary to that of cereal staples. Nutritionally it is indeed unfortunate that the Popeye saga is no longer with us. However, with the present nostalgic, escapist trend towards the diversions of a few decades back, it may well be that these cartoons will be revived. If so, they would seem to have built-in nutrition education, not only in relation to D.G.L.v. for feeding infants and mothers in less developed countries, but also possibly in relation to Olive Oyl (low-cholesterol diet) and even to Wimpy (with the hamburger epitomising a logical animal-protein/cereal " double-mix " extender of expensive meat and as a cultural disguiser of otherwise less acceptable bits of beef muscle). Caribbean Food and Nutrition Institute, P.O. Box 140, Kingston, Jamaica.
D. B.
JELLIFFE.
LIGNOCAINE HYPERSENSITIVITY SIR,-Correspondents have questioned the safety of nasal testing for hypersensitivity as advocated by Dr. Eyre and Dr. Nally (Feb. 6, p. 264). I should, however, like to correct the impression given by Eyre and Nally that lignocaine hypersensitivity is exceptionally rare. Dr. McAllen and her colleagues (May 15, p. 1024) have cited reports of a number of patients,- and I am aware of 7 more reported cases.1-4 I should like to emphasise two of the many valuable points raised by Dr. McAllen and her colleagues-that in-vivo testing may be negative although the patient is hypersensitive to a drug, and that the safest methods of investigation are in-vitro tests. I have been using, during the past 18 months, the lymphocyte-transformation technique 5,6 for testing 9 patients referred to me with a possible hypersensitivity to lignocaine after dental treatment. The lymphocyte response, estimated by the uptake of 14C-thymidine, in 4 patients yielded a significant reaction to lignocaine but not to procaine or prilocaine. Intradermal skin-tests applied in 7 patients did not show a positive reaction to any of the 3 local anaesthetics. I hesitate to draw any firm conclusions from these preliminary findings of a small series, but it seems that (a) 1. 2. 3. 4. 5. 6.
Halpern, B., Ky, N. T., Amache, N. J. Allergy, 1967, 40, 168. Holti, G., Hood, F. J. C. Dent. Practit. 1965, 15, 294. Tillman, H. H. Oral Surg. 1958, 11, 1372. Walker, R. T. Br. dent. J. 1971, 130, 2. Nowell, P. C. Cancer Res. 1960, 20, 462. Lehner, T. Immunology, 1967, 13, 159.
1246
lymphocyte-transformation tests can be positive in the absence of a skin-test reaction, as has been reported previously 1; (b) there are no attendant dangers to the patient by using an in-vitro technique; (c) subsequent use of prilocaine for local anxsthesia in 3 of the patients positive to lignocaine were free of any side-effects; (d) hypersensitivity to a variety of drugs can be incorrectly attributed to local anaathetics, particularly during dental treatment when a variety of topical agents and metallic
alloys
are
used.
Department of Oral Immunology and Microbiology, Guy’s Hospital, London SE1 9RT.
THOMAS LEHNER.
PRESENTATION OF ACID-BASE INFORMATION
SIR,-Dr. Flenley (May 8, p. 961) has produced an excellent graph and article on the method of presentation of acid-base information. His derivation of the " confidence limits of the acid-base variables from the world literature is particularly valuable, whatever form of presentation is considered the most useful and desirable. However, I remain unconvinced that the graph of hydrogen-ion activity [H+] versus carbon-dioxide tension (PC02) is any better than other more familiar graphs. Although this graph will be unfamiliar to many, it should be used if it aids understanding and allows a more uniform system for the teaching and presentation of acid-base data. I have three reasons for suggesting that the [H+] - PCÛ2 plot does not justify such a change from more frequently used "
plots. i.
The acid-base variable most often measured on patients in the wards is the total plasma-carbon-dioxide content ([COZ]), sometimes inaccurately called the bicarbonate concentration ([HC03 ]), which is measured routinely with the electrolytes and the urea. It is the variable with which clinician and student are most familiar. For a full and reliable acid-base assessment one obviously needs a measurement of two of the three variables, pH, PC02’ and [C02] on arterial blood. However, by combining the clinical information about the patient with the [C02] in venous blood one can usually decide which is the primary acid-base disturbance and make an approximate estimate of its severity. Further, if one has a few complete acid-base measurements on arterial blood one can use the more frequent daily measurement of [C02] (done with the urea and electrolytes) to assess the progress of the patient. This is especially important when complete acid-base measurements are not frequently or readily available. Enough has been said to demonstrate the dominant role of [CO2] in everyday practice and to suggest that any acid-base plot should include [C02] or bicarbonate. The inclusion of [C02] or bicarbonate as isobars in Dr. Flenley’s proposed diagram would make it a mass of confusing lines and negate its value.
My other objections fundamental:
are
less
important but
no
less
ii. Dr. Flenley mentions the difference between the in-vivo and in-vitro CO2 dissociation curves. To explain this difference to the student it is necessary to show how loss or gain of bicarbonate from the extracellular fluid can affect the relationship between [COz] (or bicarbonate) and Pco2; it is necessary, therefore, to use the CO2 dissociation curve. If one adopts the acid-base diagram suggested by Dr. Flenley as standard, the difference between the in-vivo and in-vitro curves will need to be explained in terms of [H+]. iii. For teaching purposes, at least, it would seem desirable to use the acid-base variables which can be measured. The Pco2 can be measured and is a reliable guide to the level of alveolar ventilation. The [CO2] can be measured and, with the PC02’ can give a clear picture of the acid-base status of the patient. The hydrogen-ion activity or concentration in biological fluids is unknown and not measurable by present-day techniques, although one hopes that glass-
electrode
measurements are some
function of hydrogen-ion
activity. From what I have said it is clear that I favour the
Pco2-[C02] plot for teaching purposes. Its disadvantage is that it is not linear, but this presents no real problem in teaching and in day-to-day clinical use. However, there are many who use the glass electrode in acid-base measurements for technological convenience as with the Astrup technique. For them it is plainly desirable to have a plot in which the numbers read off the pH meter can be directly inserted on the graph. I can see no reason to change from the well known and well tried ph-log Pcoz plot. It is true that when PC02 is zero the ordinate of this graph is discontinuous, being negatively infinite, but I suspect this only disturbs the sleep of the mathematical pedant. I don’t know which is the best graph to use since they all have some disadvantage, be it physiological, chemical, technological, mathematical, or psychological. It is likely that no one plot will meet all needs, and I cannot see any particular advantage of a [H+]-Pco2 plot over a pH[HC03], pH-log PC02’ or even Pco2-[C021 plot. Department of Medicine, Middlesex Hospital, London W1N 8AA.
S.
J. G. SEMPLE.
HOME HEATING AND CHRONIC BRONCHITIS
SIR,-Dr. Segall (May 22, p. 1069) states the case for adequate home heating in the prevention and the treat. ment of bronchitis, but does not discuss (1) desirable temperature levels or (2) relative humidity. Environmental warmth is, within rather wide limits, a matter of habit, and nowadays also of fashion and even of snobbery. While these last factors lead, decade by decade, to ever hotter homes, it does not necessarily follow that this " up-with-the-Jones’ " type of " our house is really properly warm " (enervatingly hot in fact) fashion is producing an atmosphere optimal for health. I suggest that in living accommodation it is unnecessary to go beyond the 62-66°F (16-6-19°C) range, and it is frankly undesirable to go beyond 70 °F (21 °C), and bedrooms should be much cooler. Relative humidity (R.H.) commonly sinks to very low levels in centrally heated premises-e.g., outdoor air at 40 °F (5°C) at 80% relative humidity, when warmed to 70°F (21 °C), yields R.H. of only 26%. Not only in Britain, but in all except very arid and very inland continental areas, the ordinary atmospheric R.H. is much higher than is generally realised. In Britain it is seldom below 60%, usually above 70%, and often exceeds 80%.1 A typical inland site, such as Munich, has average annual values at 0700 hours of 87% R.H., and at 1400 hours of 65 % R.H.2 Low values, almost down to those found in centrally heated premises, obtain in some very hot dry places-e.g. Phoenix, Arizona, with average annual R.H. at 0530 hours of 57% and at 1730 hours of 28%,3 but not everyone would consider these climates to be optimally comfortable. Low R.H. causes high evaporative water loss and drying of respiratory passages, with consequent inspissation of secretions. It is therefore important to humidify the atmosphere for people with respiratory-tract disease.4But why wait for disease ?The minimal desirable Averages of Humidity for the British Isles. Meteorological Officc no. 421. H.M. Stationery Office, 1938. 2. Tables of Temperature, Relative Humidity and Precipitation for the World. Meteorological Office no. 617; part III. H.M. Stationery Office, 1967. 3. Tables of Temperature, Relative Humidity and Precipitation for the World. Meteorological Office no. 617; part I. H.M. Stationery Office, 1958. 4. Walker, J. E. C., Wells, R. E., Merrill, E. W. Am. J. Med. 1961, 30, 259. 1.