SPECIAL EXAMINATIONS 373 



forty-eight hours at 37 C, and subculture the minute colonies 

 formed into broth, and repeat cultivation as to time and tem- 

 perature. Make films from the broth and examine micro- 

 scopically, and if found in pure culture, subject the organism 

 to the differential tests for streptococci and to nitrate broth 

 test. According to Houston, 58 per cent of the Streptococci 

 faecalis of the cow are of the lamirasacsal variety ; that is, 

 clot milk and ferment lactose, rafhnose, saccharose, and 

 salicin. It forms short chains, and is not pathogenic to 

 mice. The S. pyogenes does not clot milk, ferments 

 lactose, saccharose, and sometimes salicin, but does not 

 ferment rafhnose, and is pathogenic to mice, forms long 

 chains, and does not reduce nitrates. 



Leucocyte Test. In testing for chronic mastitis in cows, 

 Trommsdorff found that the deposit of leucocytes after 

 centrifugalizing the milk in a specially-shaped tube, was a 

 good guide as to the necessity for further investigation. 

 In an enquiry on these lines, he found 20 per cent of chronic 

 mastitis in cows, and it was associated with the presence 

 in very large numbers of capsulated streptococci. Such 

 cows give less milk The milk must be drawn directly 

 from the animal before one can say that the streptococcus 

 is from the udder of the cow. 



Centrifugauzation of Milk 

 Is used to precipitate the gross dirt, pus cells and 

 leucocytes, and bacteria. According to Scheurlen, the 

 ordinary milk bacteria in the proportion of 75 per cent 

 of them go into the cream, as do also the organisms of 

 anthrax, typhoid, and cholera. The other 25 per cent of 

 these remain in the separated milk. On the other hand, 

 tubercle bacilli are largely found in the sediment, a few 

 only passing into the cream and separated milk. 



Fermentations. 



Lactic Acid. The development of acid and curd occurs 

 normally in milk on keeping It is due to the formation 

 of lactic acid from the milk sugar or lactose, by the action 

 of enzymes produced by microbic growth. Many species 

 of bacteria are able to produce the lactic fermentation, but 

 in milk those most commonly causing it are : (1) Bacillus 



