, TESTS FOR CELLULAR CONTENT OF MILK. 129 



2. A plate culture shows colonies resembling those of strep- 

 tococci, in excess of 100,000 per cc. 



3. From ten to fifty of the colonies are transferred to broth 

 and grown 24 hours at 37 C. after which the broth cultures 

 show streptococci alone or in great excess of other bacteria 

 present. 



Slack utilizes the test also for the direct microscopic esti- 

 mation of the number of bacteria present. 



Doane- Buckley test. Doane and Buckley (10) have devised 

 a test which has been somewhat improved upon by Russell and 

 Hoffmann (8). The technic given below is that described by 

 the latter writers : 



COLLECTION OF SAMPLE. 



Sample for analysis should be taken from the entire milking of the 

 animal, as the stoppings contain a somewhat larger number of cells than 

 other portions of the milk. For the purpose of examination take 200 cc. 

 in stoppered bottle. 



TIME INTERVAL, BETWEEN COLLECTION AND ANALYSIS. 



To secure satisfactory results, milk must be examined in a sweet con- 

 dition. Development of acidity tends to precipitate casein in the milk, 

 and thus obscure the examination of microscopical preparations. Sam- 

 ples received from a distance can be preserved for satisfactory microscop- 

 ical examination by the addition of formalin at time of collection, 

 proportion of 1 cc. to 250 cc. of milk. Formalin has been found the best 

 preservative to use, although it causes contraction of the cells to some 

 extent. 



PROCEDURE WITH REFERENCE TO PREPARATION OF SAMPLE. 



1. HEATING SAMPLE. 



To secure the complete sedimentation of the cellular elements in the 

 milk, it is necessary to heat the same to a temperature which will break 

 down the fat globule clusters, or lessen the ordinary creaming properties 

 of the milk. Samples should be heated at 65 to 70 C. for not less than 

 ten minutes, or from 80 to 85 where very short periods of exposure 

 (one minute) are given. This treatment causes the more homogeneous 

 distribution of the fat globules through the milk, and when the sample 

 is then subjected to centrifugal force the cell elements are not caught in 

 the rising fat globules, but on account of their higher specific gravity are 

 concentrated in the sediment by centrifugal force. 



