412 APPLIED BACTERIOLOGY 



infection. In experiments of this kind care should be 

 taken to procure several specimens of the filter under 

 examination, and to ascertain that they fairly represent 

 those intended for ordinary use. It is also desirable, when 

 special test-organisms are artificially introduced, to avoid 

 the simultaneous introduction of small quantities of culture 

 material. 



It has been found that water and other fluids sterilised 

 by heat may retain a toxic capacity, setting up, for instance, 

 suppuration on inoculation into suitable animals ; while 

 the same liquid sterilised by filtration through a Pasteur- 

 Chamberland tube produced no effect. At the present 

 time these phenomena and the conditions which determine 

 them are not sufficiently worked out to make it possible for 

 filters to be adequately examined as to their capacity to 

 produce similar results. 



A very full and interesting report by Drs. Woodhead 

 and Cartwright Wood upon the efficiency of the various 

 types of filters in use will be found in the British Medical 

 Journal, vol. ii., 1894, pp. 1053, 1118, 1182, 1375, 1486. 



THE EXAMINATION OF MILK. 



From the fact that milk forms such an excellent nutrient 

 material for the growth of nearly all bacteria, it follows 

 that this article of food is almost invariably contaminated 

 with bacteria from various sources. The milk in the udder 

 of a cow in perfect health is absolutely free from micro- 

 organisms, but when the cows are suffering from disease 

 the milk as it leaves the udder may contain the tubercle or 

 other pathogenic organisms which may be, and generally 

 are, the specific cause of the particular diseased condition. 

 It is unquestioned that many diseases, such as scarlet fever. 



