744 A MANUAL OF BACTERIOLOGY 



are almost useless (except in cases of advanced tuberculosis of 

 the udder or when the milk of a single cow is examined), and 

 inoculation must be performed. At least 250 c.c. of the milk 

 should be centrifuged at 2,000 to 2,500 revolutions per minute 

 for an hour. As many organisms become entangled in the 

 cream, it is advisable to stop the machine after half an hour, 

 stir in the cream, and again centrifuge. The fluid is poured or 

 pipetted off carefully, so as not to disturb the sediment, leaving 

 about 3 c.c. in the tube. The sediment and the remaining fluid 

 are then well mixed, and about 1 c.c. is inoculated subcutaneously 

 and intraperitoneally into two guinea-pigs respectively (see also 

 p. 398). For staining, a process of solution of the milk may be 

 employed, 20 c.c. of the milk being mixed with 1 c.c. of a 50 per 

 cent, potash solution, and heated in a water-bath until the solu- 

 tion turns brownish ; 20 c.c. of acetic acid are then added. The 

 mixture is shaken, heated in a water-bath for three minutes, and 

 centrifuged for ten minutes. The fluid is poured off, 30 c.c. of 

 hot water are added to the sediment, and the mixture is again 

 centrifuged. Films are then prepared from the sediment, and 

 stained for the* tubercle bacillus (see also p. 393), the films being 

 always treated with alcohol as well as with acid. 



Non-pathogenic acid-fast bacilli occur in milk (p. 409). 



2. The diphtheria bacillus is searched for by making serum 

 cultures from, and inoculating guinea-pigs with, the sediment. 

 If a diphtheroid organism is detected it must be isolated and 

 examined by culture tests and animal inoculation. 



In milk and cheese a bacillus is frequently met with closely re- 

 sembling the diphtheria bacillus in its morphological and cultural 

 characters ; it is, however, quite non-pathogenic. 1 



3. The typhoid, paratyphoid, Gartner, and dysentery bacilli 

 and cholera vibrio may be searched for by the methods given for 

 "Water." 



4. The M. pyogenes and the Streptococcus pyogenes may be 

 searched for by means of plate cultures on glycerin agar. 



5. Examination of sediment. Houston and Savage (loc. cit.) 

 have devised methods for the quantitative estimation of the 

 sediment by centrifuging in special graduated tubes. For the 

 microscopical examination of the sediment the milk is centrifuged 



1 See Scientific Bidl. No. 2, Health Dept., City of New York, 1895, p. 10. 



