On the Biological Examination of Water and Milk. 35 
etc., is still a disputed one, but obviously it depends very 
much on the precautions taken by the attendant himself, 
and accidental contamination of foods and drinks by such a 
person must not be lost sight of. 
B. Contamination of Milk.—With reference to milk con- 
tamination, it is self-evident that the various ways in which 
water may be contaminated apply also to milk, and with 
even greater force, for milk is an excellent nutrient medium 
for germs of nearly all kinds, where they not only feed and 
live, but multiply abundantly. Milk may be contaminated 
in at least two other ways, viz.—(1) by the addition of 
typhoid contaminated water for purposes of adulteration ; 
and (2) by the defective scouring of milk-vessels with 
infected water.! ; 
Having thus briefly glanced over the various ways in 
which two of our commonest drinks may be so easily 
infected, I pass on now to consider the various methods 
which have been employed for detecting and isolating the 
specific germ of typhoid fever. 
I have already drawn your attention to the fact that the 
_ discovery of Eberth’s bacillus in water or milk establishes at 
once the previous existence of a case of typhoid fever, no matter 
what value we attach to the bacillus itself, whether it be 
the cause, concomitant, or effect of the disease. 
To Robert Koch we owe the unique method of “plate” 
cultivation for the isolation of micro-organisms inextricably 
mixed up with each other. His method consists in inoculat- 
ing tubes of melted nutrient gelatine with the suspected 
material, diffusing the latter uniformly throughout the tubes, 
and then pouring out the gelatine contained in them upon 
sterilised glass plates, with certain precautions against con- 
tamination by aerial organisms. The glass plates are placed 
in moist chambers in order to prevent the gelatine becoming 
too dry. The various organisms are thus spread out on flat 
surfaces, being held in position by the solidifying of the 
1 Another mode of contamination of the milk has been suggested, but has 
not found much support, viz., the direct secretion of the typhoid poison 
along with the milk; but it seems extremely improbable if any animal could 
have organisms multiplying within its body and yet remain unaffected. 
