634 Proceedings of the Royal Society of Edinburgh. [Sess. 
Returning to Miss Chick’s problem, the following remarks at once 
suggest themselves. In her paper the living organism is shown to act 
towards disinfectants as if it were itself a chemical substance. Thus the 
actual numbers of anthrax spores living after a specific period is in a 
geometrical progression. It is the same problem as if the whole population 
of a district were uniformly at the same instant exposed to an infective 
disease, and the uniform medium of infection kept constantly present in the 
same amount. In this case an epidemic curve would be, on her analogy, given 
by x = ae ~ pt ‘ I n the cases here considered, however, it is some substance 
contained by the organism which is assumed to obey the mono-molecular 
law, and in each case a different kind of substance. 
Her case is really in a different dimension from those given in this 
communication. She indeed touches on the general problem when she 
discusses the behaviour of Bacillus paratyphosus, and shows that the 
difference of age in the organism makes a great difference in the rate of the 
action. Thus the old organisms die more quickly than young, and thus the 
numbers living no longer obey the exponential law ; but the data she gives 
are not sufficient to find the law of death even approximately. 
I do not propose to carry this further at the present moment. The 
examples chosen are the chief obtainable. Those in case 2 are the most 
subject to criticism as selected. It is essential, however, that in this class 
we have equal freedom of infection, and that the disease be definitely 
infectious in a homogeneous population. Other diseases, such as enteric 
fever, do not seem to fulfil the conditions sufficiently. It can hardly be 
expected that the whole progress of immunity and mortality during life 
should be comprehended in one chemical law. 
REFERENCES. 
(1) Arrhenius, Immuno- Chemistry, pp. 5-6. 
(2) Brownlee, “The Law of the Epidemic,” Proc. Roy. Soc. Ed., June 1906. 
(2) Brownlee, “The Mathematical Theory of Epidemic Distribution and 
Random Migration,” Proc. Roy. Soc. Ed., May 16, 1910. 
(3) Chick, “ An Investigation of the Laws of Disinfection,” Journal of Hygiene, 
1908, vol. viii. p. 92. 
(4) Brownlee, Rep. of City of Glasgow Fever Hosp., Belvidere , 1901-2, 1902-3. 
(5) Report of Royal Commission on Vaccination. Appendix on Gloucester. 
(6) Murchison, Continued Fevers of Great Britain, p. 237. 
(7) Barry, Report on Epidemic of Small-pox in Sheffield in 1887-8. 
(8) Brownlee, “Small-pox and Vaccination,” Biometriha, vol. iv. p. 313. 
{Issued separately September 28 , 1911 .) 
