PSEUDO-TUBERCLE BACILLI 85 



When it comes to tlie examination of milk of normal 

 appearance, the question is usually more difficult, be- 

 cause the number of tubercle bacilli is less. A direct 

 microscopic examination of the milk is rarely useful ; it 

 is better to pour a little of it on a dark surface and pick 

 out with a needle the small flakes which are usually 

 present and form the little lumps of fibrous exudate to 

 which the bacilli adhere. Still better results are reached 

 by centrifuging the milk and examining the sediment. 

 Any milk centrifuge may be used for this purpose (in- 

 cluding those used for determining the amount of fat) 

 and it may be driven by steam or by hand power. Of 

 course, a large centrifuge of high speed is best. 



Instead of the centrifuge, the separation of tubercle 

 bacilli by other means has been suggested. 



For this purpose Biedert employs the following 

 method : 100 c.c. milk are mixed with 4 to 8 drops of solu- 

 tion of sodium hydroxide; the mixture is well shaken 

 until the small flakes and lumps are dissolved, then it is 

 boiled. The cloudy fluid is poured into a conical glass 

 and left standing for some time. The sediment that 

 collects in the point of the glass may be drawn off by a 

 pipette and examined microscopically. 



The practice has also been followed of submitting the 

 milk to special treatment with chemicals before it is 

 centrifuged. 



Thus, Ott mixed together 25 c.c. milk, 2 c.o. concen- 

 trated ammonia water and 100 c.c. of a mixture of equal 

 parts of ether and petroleum ether, in a separator flask 

 with a glass stopper. After being shaken and allowed 

 to stand, the ammonia-casein solution, in which the 

 bacilli are found, is drawn off from the bottom and 

 centrifuged. 



Hammond's method is as follows : 100 c.c. of milk are 

 mixed with 5 c.c. of phenol ; 15 to 30 c.c. of the mixture 



