Counting Bacteria. 925 



objective, indicates the following number of bacteria for the 

 various fields which are designated by letters : 



In 1/4 of square a = 40,000,000 per c. c. of milk 

 In 1/2 of square a = 20,000,000 per c. c. of milk 

 In total square a = 10,000,000 per c. c. of milk 

 In 1/4 of square b = 8,000,000 per c. c. of milk 

 In y 2 of square b = 4,000,000 per c. c. of milk 

 In total square b = 2,000,000 per c. c. of milk 



In circle c = 1,000,000 per c. c. of milk 



In total field of 



observation = 800,000 per c. c. of milk 



The total number of bacteria found in all the counted fields 

 is multiplied by the relative number corresponding to the field of 

 the size that was counted and divided by the number of counted 

 fields. If, for instance, in 20 ocular fields of size "a" Skar found 

 the number to be 150 bacteria, then these figures give : 



15QX 20 >000 ' Q Q = 150X500 > 000 = 75 > 000 > 000 per c. c. of milk. 



Skar always found many more bacteria by this method than 

 were found by the plate method (2 to 70 times as many). 



The direct counting is more rapid and more accurate than 

 the plate counting method. 



As already mentioned, for practical control work the counting 

 of bacteria may be omitted. In this work the reductase test offers 

 a quicker determination of the spoiled condition of the milk. 



For special examinations the following methods are recom- 

 mended: For determining age and decomposition the reductase 

 test and periodically repeated acid tests, besides the microscopical 

 examination of the sediment, should be applied. 



For determining decomposition of pasteurized milk, the per- 

 oxydase test, in combination with the reductase test, and, at times 

 also the catalase test and microscopic examination of the sediment, 

 should be used. 



For the judgment of dirty milk, the determination and esti- 

 mation of the dirt content, the reductase test, periodical acid test 

 and microscopic examination of the sediment should be made. 



Inflammation of the Udder. 



(a) Market milk: 



1. Determination of the quantity and appearance of 



the centrifugal slime. 



2. Microscopic examination of the sediment for 



parenchyma cells and the presence of animal 

 forms of streptococci. 

 3. In tuberculosis : Inoculate. 



(b) Individual samples: 



1. Trommsdorff test. 



15 



