32 Proceedings of the Royal Physical Society. 
III. On the Biological Examination of Water and Milk with 
special reference to Typhoid Fever. By G. CARRINGTON 
Purvis, M.D., B.Sc. Edin. 
(Read 18th March 1891.) 
Not many years ago the examination of water, air, or soil, 
in so far as the search and isolation of germs of disease were 
concerned, was a thing unknown, indeed the fact of living 
bodies being in any way the cause of disease was called in 
question; but, thanks to the labours of Pasteur, Lister, 
Koch, and others, there is not now the shadow of a doubt, 
that some at least of the deadly diseases are due to the 
presence of a living germ or parasite within the animal body. 
Take, for instance, that, very fatal disease known as wool- 
sorter’s disease or anthrax; this was shown years ago by 
Pasteur to be due to a microscopic organism or microbe 
known as the Bacillus anthracis, or again that very common 
disease known as phthisis, or pulmonary consumption (with 
which we are all more or less familiar). This disease was 
shown, by the beautiful researches of Koch, to be due to a 
very minute organism known as the Sacillus tuberculosis, or 
tubercle bacillus. Both these diseases—anthrax and tuber- 
culosis—can be artificially reproduced in animals by the 
inoculation of the smallest portion of the living colonies 
erown outside the body, it may be, for several generations, 
and thus the cause of these two diseases is experimentally 
demonstrated ; and by the same methed of inoculation, acci- 
dental or otherwise, a few other micro-organisms, e.g., bacilli 
of elanders, have been proved to produce disease in man and 
the lower animals. 
When, however, we come to consider typhoid fever, cholera, 
and other diseases to which the lower animals are not, as a 
rule, susceptible, the question of a particular organism causing 
a particular disease is open to doubt, for in these diseases the 
direct or experimental method of demonstration by inocula- 
tion fails. If, however, a particular organism is always 
associated with a particular disease, and is not met with in 
any other disease, then there can be only three alternative © 
explanations,—either the organism is the cause of the disease, 
