1. A quantitative theory has been developed for the reactions between antigens and antibodies, applicable in particular to the precipitin reaction. The theory is equally applicable to unspecific precipitations, for instance the reaction between proteins and protein precipitating agents such as nucleic acids, etc.

2. The theory is based on the concept that the antigen-antibody interaction is governed by the same principles as the dissociation of a polybasic acid, HNT, where the antibody corresponds to the hydrogen ion H, and the antigen to the anion T. In their mutual reactions the antigen G is supposed to be polyvalent and the antibody A monovalent: hence the result of the interaction is a mixture of compounds ANG, AN-1G, …, AG.

3. A mathematical deduction is performed starting from the law of mass action, which leads to expressions for the amounts of total precipitate and its constituents in terms of the quantities of antigen and antibody which were mixed and the known equilibria constants.

4. A numerical example is given for a tetravalent antigen. Three cases are represented in graphical forms: the ‘X case’ without inhibition zones, the ‘Y case’ with one and the ‘Z case’ with two inhibition zones. Certain characteristics are described and the significance of the ‘equivalence point’ is analysed.

5. A discussion deals with the irreversibility in relation to the Danysz phenomenon and the dilution effect, and finally the parameters of the theory are more closely considered.

The quantitative theory for the interaction between antigen and antibody presented in the previous paper has been compared with some experimental precipitin reactions published in the literature. These reactions include Type VIII pneumococcus polysaccharide-homologous (horse) antibody, egg albumin-(rabbit) anti-egg albumin and diphtheria toxin-(horse) antitoxin.

1. The general course of the experimental precipitation curves (total amount of precipitate, amounts of precipitated antigen and antibody) corresponded well to the theoretical type curves. Hence it may be concluded that the precipitates may be composed of mixtures of compounds of the types AG, A2G, A3G, …, ANG in accordance with the law of mass action. In the cases with ‘inhibition zones’, however, AG, or ANG, or both (and perhaps several more compounds) retain the same solubility as the free antigen (G) and free antibody (A).

2. With regard to the location of the ‘equivalence zones’, experiment and theory also showed a satisfactory agreement.

3. A hypothesis on the velocity of flocculation in the precipitin reaction is presented and compared with some recent results. The relation between the immunological concepts ‘equivalence (neutral) point’, ‘optimum point’ and ‘maximum precipitation point’ is also discussed.

1. The virtual sterilization time (v.s.t.) has been used as a measure of the rate of disinfection of Bact. coli cultures by phenol under carefully standardized conditions, and the relationship between this rate and temperature at five phenol concentrations has been examined.

2. The graphs of log (v.s.t.) against temperature reveal that the formula t×θT = A, as usually employed for the calculation of the temperature coefficient of the rate of disinfection, has only a limited applicability for these data. θ and Q10 increased with temperature especially at high concentrations, and at the lowest concentration there was a tendency for them to increase again as the temperature was reduced below a certain point.

3. The other general type of formula, t(T –α)b = a, used for the calculation of biological temperature coefficients, is also of very limited value when applied to these data since b increases with temperature at all concentrations.

4. The magnitude of these temperature coefficients and their manner of variation are considered in relation to previously published data by other authors and the way in which θ should theoretically vary with temperature is discussed.

1. The virtual sterilization time (v.s.t.) has been used as a measure of the rate of disinfection of Bact. coli cultures by phenol under carefully standardized conditions. The relationship of this time to temperature at each of five phenol concentrations has been examined from a fresh point of view, since it has previously been shown (Jordan & Jacobs, 1946) that none of the commonly accepted temperature coefficients was satisfactorily constant.

2. The relationship is such that a minimum or threshold temperature exists for each concentration. A corresponding ‘maximum’ temperature has been fixed, defined as the temperature at which the v.s.t. is 10 min. The value of (v.s.t. – 10) thus varies from infinity to zero between these temperature limits.

3. Sigmoid curves are obtained when log (v.s.t. –10) is plotted against temperature for given phenol concentrations. These may be regarded as asymptotic to ordinates at the minimum and maximum temperatures.

4. The Pearl-Verhulst logistic equation gives a curve of the required sigmoid type, and this formula has been shown to fit the curves of log (v.s.t. – 10) against temperature very satisfactorily over the range of concentrations studied.

5. One of the constants of this formula partakes of the nature of a temperature coefficient, and it has, therefore, been possible to derive a truly constant temperature coefficient for each phenol concentration.

6. The values of this new temperature coefficient do not vary greatly with phenol concentration within the range studied, but it is not yet possible to establish whether it is essentially constant for all phenol concentrations with which it is possible to work.

1. Avian tubercle bacilli were grown in hanging-drop cultures in embryo extract prepared as for tissue culture, but diluted to 25–5% of its usual concentration.

2. Microscopic branching colonies of pseudomycelia developed in the surface film of the hanging drops during the first few days of incubation, after which growth declined.

3. The development of these colonies was studied on the warm stage and proceeds as follows:

(a) The original rods elongate into filaments.

(b) The filaments multiply by ordinary fission and also by forming fine, pin-like terminal sprouts which grow into independent bacilli.

(c) After division the daughter filaments usually remain in contact at the site of fission; their terminal growth continues at an angle to the former cleavage plane and the colony thus acquires its characteristic branching structure.

(d) The colony enlarges and ramification becomes increasingly complex until about the fifth day of incubation when growth declines. The bacilli remain filamentous.

4. When transferred to embryo extract of normal concentration the pseudomycelial colonies revert to the ‘standard’ type of development characteristic of the more concentrated medium, i.e. they pass through a phase of filamentous proliferation followed by disintegration of the filaments into short discrete rods.

5. The development of a pseudo-mycelium is compared with the three common types of growth previously seen in more concentrated embryo extract.

6. The results of this investigation shed light on the controversial question of whether the ‘mycelial’ form of the tubercle bacillus is a single individual formed by ‘true’ lateral budding or a composite structure produced by the terminal, angular growth of coherent but independent bacilli. Our observations on the living organisms have shown that under appropriate experimental conditions both these forms may develop.

1. A series of lactic streptococci which were almost all capable of clotting milk in 24 hr. at 22°C. were divided into two groups on the basis of a few simple biochemical and morphological tests. The two groups corresponded to what some workers consider to be the species Str.lactis and Str.cremoris.

2. A series of phage races were tested for their action on the streptococci under various temperature and growth conditions.

3. The characteristics of phage attack on the organisms tended to confirm the division into Str.lactis and Str.cremoris species. Each of the strains of the long-chained cremoris type was attacked by only a few phages at the most, sometimes by a single phage only, whereas each of the lactis (short-chained) strains was attacked by a variety of phages. Furthermore, with two exceptions, the phage attacking the cremoris types on the one hand and the lactis types on the other formed quite separate and distinct groups.

4. None of the phages acted upon the several available strains of Str.faecalis and other group D (Lancefield) streptococci.

5. The evidence obtained from the phage sensitivity tests seems to justify the division of the lactic streptococci into two species, Str. lactis and Str. cremoris.

The author is indebted to Dr H. R. Whitehead for his interest in this work, and for helpful criticism and advice.

The experiments reported below followed the observation that living dysentery bacteria (S-variant) are not agglutinated after 4 hr. contact with an homologous antiserum. Somewhat later agglutination appears, but does not reach the end-titre. The next day fine granula are visible on the bottom of the test-tube which are readily dispersed by gentle shaking. This form of agglutination was designated ‘soft’. If the bacteria are heated for 30 min. at 100°C. agglutination appears within 2 hr. at all dilutions up to the end-titre of the serum. The next day a heavy sediment is visible, and in low serum dilutions a cuticula covers the bottom of the test-tubetities injected intravenously were 0·1, 0·25, 0·5 and 1·0 mg.; the latter were relatively harmless and quantities of 0·2–2·0 mg. were injected.

A high proportion of young men in this country suffer from premature baldness. Alopecia is not a disease entity but one of the outstanding features of chronic fluorine poisoning (fluorosis). It is frequently associated with dystrophies of other organs of ectodermal origin, namely, those of the skin and its other appendages, the teeth and nails. Since all these organs are regulated by the parathyroid glands, it is concluded that alopecia, too, is produced by fluorine acting through the medium of these endocrine glands. By its ability to precipitate the calcium content of the body, fluorine may lay the foundation for alopecia already in intra-uterine life, or produce it at any time after birth.

The action of fluorine is closely similar to that of thallium. There is ample evidence to show that in both fluorosis and chronic thallium poisoning the vegetative nervous system is vitally involved.

Toxic alopecia due. to fluorine is preventable.

Enteric fever occurs in both temperate and tropical countries, and its spread depends mainly on the sanitary conditions prevailing, on the degree of purity of the drinking water, particularly in the country districts where no general water supplies exist, and on the degree of efficiency of the sewage disposal systems.

Three major factors determine the tropical fitness of fabrics: (1) thermal insulation, (2) porosity, (3) reflecting power.

The laboratory method here outlined and utilized by us over the past 11 years, of examining and judging ice-cream on a milk basis, appears to pro-vide a sieve of mesh generous enough to let through the passably ‘fit’ while stopping the presumably ‘doubtful’ and ‘unfit’.

Eighty-six samples of Alexandria milk ice-creams collected from various vendors in the city by Army Inspectors during the autumn months of 1944 showed, on this method, about 19% ‘unfit’—a result in remarkable agreement with fifty-eight samples from Municipal sampling, collected earlier in the year during summer months, which showed 16% ‘unfit’.

A small number of samples collected after hygienic control of the process of manufacture by Army Inspectors resulted in a total disappearance of unfit samples. The improvement arising from this controlled experiment was estimated at a lowering of 60% in total bacteria per c.c., and a reduction of 77% in coliforms.

The results of the latter experiment show what good results can be achieved in the betterment of milk ice-creams by simple hygienic measures, and should be more widely known in all centres where members of the Services are large consumers of ice-cream.

Acknowledgements are due to Lieut. J. T. S. Templeman, R.A.M.C., and his staff for their part in this investigation; and to Lieut.-Col. G. P. M. Marshall, R.A.M.C., A.D.H., for instigating the experiments on hygienic control of production.

1. The problem of louse control by powders has been shown to be twofold, namely (a) to kill the lice present on a verminous person at the time of treatment, and (b) to prevent reinfestation of a deloused person or infestation of a clean person. In these experiments no single insecticide was found that would fulfil both functions.

2. The work shows the necessity of using laboratory tests (‘cell tests’) in conjunction with insecticide tests on the parasite living under natural conditions (‘field trials’).

3. The technique and results of the cell tests and the field trials are described in detail. In the field trials naturally louse-infested persons living in verminous surroundings were treated and examined daily to observe the true insecticidal value of each preparation.

4. Naphthalene was found to be the most effective insecticide for killing body lice quickly. It failed to give any protection against reinfestation.

5. The vegetable insecticides, derris and pyrethrum, were found to be toxic to Pediculns humanus corporis, but either alone or in combination with each other they were inferior to other combinations of insecticides.

6. The combination of high-boiling tar acids and derris resulted in the combined chemicals being more toxic to lice than either alone. This proved an activation effect, and the theory of activation is discussed.

7. Activated derris, while slow in killing lice, was shown to be the best preparation which gave protection against reinfestation.

8. The preparation referred to as A.L. 63 was outstanding as the best preparation that controlled body lice and which fulfilled the original conditions stipulated for a successful louse powder for human use. The formula is:

H.B.T.A. 2 %

Derris root 14·3 % giving 1 % rotenone and a minimum of 3 % extract in the final product

Naphthalene 50·0 %

China clay 33·7 %

The nature of each chemical in this formula is defined.

9. A.L. 63, when applied to the clothing of a verminous person, killed 95% of all lice on the treated garment in 24 hr., and gave complete protection against reinfestation for an average of 5 days, and partial protection for 8 days. When applied to clean garments as a prophylactic measure, A.L. 63 gave complete protection for an average of 7…8 days, and partial protection for approximately 16 days.

10. Patients living in a verminous environment were made to wear one shirt continuously for a month without washing it. Even under these conditions they were protected from infestation by treatment of the inside of the shirt, at 8-day intervals, with A.L. 63.

11. A short history is given of the use of A.L. 63 in the British army from 1940 to 1944.

During this work we have had much help and sympathy from many people, but we would like to place on record our especial thanks to the following: Prof. P. A. Buxton, of the London School of Hygiene and Tropical Medicine, for supplying us with the original material for establishing a louse colony, and for his great interest and encouragement during the work; Dr W. E. Parry, the Divisional Police Surgeon at Spitalfields, for his kindness in describing the best areas to search for suitable patients, and his assistance in finding suitable accommodation for establishing the ‘clinic’; those numerous volunteers, within the Cooper, McDougall and Robertson organization, who offered to feed lice when the colony was being maintained at the Research Station, and suffered much discomfort while doing so.