THE GRADING OF MILK 



159 



follows : 10 c.c. of the milk are introduced into a glass tube, the 

 end of which is drawn out into a capillary graduated in thousandths 

 of a cubic centimetre. The tube is closed by a rubber stopper and 

 whirled at a speed of 1200 revolutions per minute. Normal milk 

 will generally yield a sediment measuring 0-002 to 0-004 c.c., 

 while milk drawn from diseased udders will yield a sediment 

 measuring 0-01 c.c. or even more. The amount of the sediment 

 is, however, not a decisive criterion by itself ; the test must be 

 supplemented by a microscopic examination, and only in cases 

 where large numbers of bacteria characteristic of udder disease, 



FIG. (34. Leucocyte Sediment from the Milk of a Cow suffering from 

 streptococcic mastitis. (After Ernst.} X 1000. 



e.g., streptococci, are found can definite conclusions be drawn. 

 As these bacteria cannot be distinguished from the harmless milk 

 bacteria by direct inspection 1 , the test is only of value when 

 applied to milk fresh from the cow, and can therefore only be 

 applied as an aid to veterinary control at the farm. In mixed 

 milk the characteristic features are completely lost on account 

 of the dilution alone. 



THE CATALASE TEST 



This test is supplementary to the leucocyte test. The various 

 constituents of blood, especially the corpuscles, are rich in catalase ; 



1 Capsule formation and disc-like cells, which by some authors are 

 regarded as characteristic of Sc. mastilidis, can be observed in all strepto- 

 cocci. On the other hand, as already mentioned under Sc. mastitidis, the 

 red colour in casein starch stab cultures is very characteristic. 



