THE CONTENT OF PATHOGENIC GERMS. 209 



to unfavourably influence the ripening process of the cheese pre- 

 pared therefrom. In fact, until we are in a position to introduce 

 and carry on this process to its completion in a reliable manner 

 by artificially added ferments, the above-named requirement must 

 necessarily remain unfulfilled. Fortunately the acid produced by 

 the ripening process forms an effective antidote, which checks the 

 development of the pathogenic organisms. H. WEIGMANN and 

 G. ZIRX (I.) proved that Bacillus (vibrio} cholera asiaticce perished 

 within twenty-four hours when artificially inoculated on cheese. 



As will be gathered from the preceding observations, the 

 sterilising of milk samples destined for the cultivation of organisms 

 in the laboratory is a very troublesome operation, since this necessi- 

 tates an absolute freedom from germs. In order to obtain this 

 result, the samples are exposed for ten to fifteen minutes to steam 

 under pressure, at a temperature of 120 C. The decompositions 

 hereby induced have no injurious effect in some cases ; nevertheless 

 when delicate organisms are to be cultivated that would not thrive 

 in milk thus altered, a method of mixed sterilisation must be 

 practised. A little ether or chloroform is added to the sample, 

 allowed to react for a short time, after being thoroughly shaken 

 up, and, at the end of two or three days, disinfection is effected 

 by placing the sample for twenty to thirty minutes in the steamer 

 (at 100 C.). The statement, often met with in books, that 

 milk may be sterilised by exposure to the action of a current 

 of steam at 100 C. for twenty to thirty minutes on three succes- 

 sive days, is (according to the author's experience) deceptive. If 

 such "sterilised" milk be placed in the incubator, an effluvial 

 decomposition, with copious development of potato bacilli and the 

 like, will be noticeable in nine cases out of ten. 



A number of bacterium poisons the suitability of which has 

 been made the subject of comparative investigation by J. NEU- 

 MANN (I.) and M. KUHN (I.) have been proposed for preserving 

 milk that is to be sent to a laboratory for the purpose of having 

 its fat content ascertained. The potassium permanganate, formerly 

 recommended, behaved badly under the ordeal, whereas, on the 

 other hand, potassium bichromate (for the use of which for the 

 purpose in question Alen has taken out a patent) proved reliable 

 in cases where it was a matter of preserving milk that was still 

 sweet. The sample is treated with an admixture of 0.5 gram 

 of pulverised K 2 Cr 2 7 (or with 5 c.c. of a 10 per cent, solution of 

 this salt) per litre, the dilution produced in the latter case exer- 

 cising no appreciable influence on the accuracy of the fat deter- 

 mination. If the milk at the moment the sample is drawn is 

 already somewhat sour, then an addition of ammonia 3 c.c. of a 

 27 per cent, solution of ammonia per litre of milk will be 

 preferable. 



Not infrequently milk intended for sale is qualified with sub- 

 stances acting as poisons towards bacteria, with the idea of 



VOL. I. O 



