86 MILK HYGIENE 



are placed into two tubes and centrifuged for 15 min- 

 utes. The fluid is poured off and 3 c.c. of a 5 per cent, 

 solution of potassium hydroxide are added to the sedi- 

 ment. After violent shaking, the liquid is allowed to 

 stand 2 to 3 minutes, then 15 c.c. of water are added to 

 it ; it is shaken and centrifuged 20 minutes. Then, 15 c.c. 

 of the liquid are drawn off from above, while the residue 

 is examined microscopically in the usual way. 



The detection of tubercle bacilli in milk by cultiva- 

 tion is most difficult and without practical utility. In 

 doubtful cases, where the result of the microscopic exam- 

 ination is uncertain, it is advantageous to " harpoon " 

 the udder, thereby removing a small sample of the deep 

 tissue of the udder for examination microscopically or 

 by the inoculation of experimental animals, as guinea 

 pigs. 



Statements of the temperature at which tubercle 

 bacilli are killed, vary greatly. While, in the first in- 

 stance, Bang and other investigators found that momen- 

 tary heating to 85 C. killed, Legay and Bech reported 

 that brief boiling was not always sufficient, and Volsch 

 found that even repeated boiling would not always kill 

 tubercle bacilli. On the other hand, Th. Smith reached 

 the conclusion that even a far lower temperature than 

 those originally given would kill with certainty if the 

 formation of a pellicle during heating was prevented. 

 According to the most recent investigations, carried out 

 with the greatest accuracy by Bang and Stribolt, it is to 

 be considered as proven that heating at 65 C. for 5 

 minutes or momentary heating at 70 C. kills the bacilli 

 with certainty and that the former uncertainty on this 

 subject arose principally from faulty methods in the 

 experiments. The observations by Legay, Bech and sev- 

 eral others show, however, that in practice a very 

 high degree of heat must be attained to be safe, and that 



