EXAMINATION OF MILK 743 



The Boas-Oppler bacillus, met with in the stomach in cases 

 of carcinoma of that organ (p. 687), appears to be identical with 

 the B. bulgaricus. 



Examination of Milk 



Number of organisms per cubic centimetre, This is carried out 

 by diluting the milk to 1 in 1,000-1 in 1,000,000 with sterile water, 

 or preferably nutrient broth, as a better mixture is obtained. 

 Plates are then made either in gelatin or in distilled water agar 

 (1| grm. powdered agar, distilled water 1 litre, Eastes), or pre- 

 ferably in both media. 



Breed and Brew count the organisms directly. With a special 

 pipette, 0-01 c.c. of milk is deposited on a slide, the droplet of 

 milk is spread evenly with a stiff needle over an area of one square 

 centimetre, and the slide is dried quickly in a warm place. When 

 dry, it is treated with xylol for one to a few minutes, then treated 

 with 80 per cent, alcohol for one to a few minutes, and is then 

 transferred to a fresh saturated aqueous solution of methylene 

 blue in which the slide remains for from five to sixty seconds. 

 The film is then rinsed with water and decolorised with alcohol 

 to the required degree. The slide is finally dried, and the film is 

 examined directly with the oil-immersion lens. The organisms 

 and cells in 100 fields are then counted, and, knowing the area 

 of the field (which must be ascertained), the total number of 

 organisms in 1 c.c. of the milk can be calculated. The pipette 

 is of the hsemocytometer pattern and should be calibrated with 

 mercury to contain 0-0104 c.c. to allow for the loss of milk due 

 to adhesion to the glass (0-0104 c.c. of mercury = 0-1423 grm.). 



B. coli, B. Welchii, and streptococci. These are searched for 

 quantitatively by the methods detailed for "Water" (pp. 710, 

 711). Amounts of milk in decreasing decimal order from 100 c.c. 

 to 0-000001 c.c. should be examined. The B. coli must be differ- 

 entiated from B. lactis aerogenes and B. acidi lactici (see table, 

 pp. 450 and 452, and p. 464). 



Pathogenic organisms. The detection of these, with the excep- 

 tion of the tubercle bacillus, is difficult and uncertain. In all 

 cases the milk should be centrifuged and the deposit examined. 



1. For the detection of the tubercle bacillus x staining methods 



1 See Delepine, Rep. Med. Off. Loc. Oov. Board for 1908-09, p. 134. 



