I 4 2 MILK AND ITS HYGIENIC RELATIONS 



to render the method reliable. The cell-count obtained by the 

 use of the direct method was much higher than that obtained in 

 the same sample of milk by the use of the other methods. These 

 authors believe that the average number of cells present in milk 

 is probably not less than 1,500,000 per c.c. 



Hewlett, Villar and Revis used about six drops of formalin to 

 60 to 70 c.c. of milk before centrifuging, prior to staining, and to sub- 

 sequent counting of the cells. They state that they compared this 

 method with the heating method suggested by Russell and Hoff- 

 mann and found that the two methods gave very similar results. 

 They suggest that the action is due to a disruptive effect on the 

 clusters of cells themselves, and consider it possible that heat or 

 formalin break down aggregations of cells by destroying some 

 agglutinating property rather than by an action upon the fat 

 clusters. The destruction of the agglutinating substance would 

 thus produce a more even distribution of the cells and cause an 

 apparent numerical increase. They add that the carrying power 

 of fat globules not only for cells but also for blood, bacteria, etc., 

 may be broken down by either heat or formalin. 



These authors have also carried out investigations upon the 

 best fluid to use for washing the cells. 



Ross (1912) heated the milk investigated by him for cellular 

 content to ioo-i20 F. Ten c.c. of the milk was then centrifuged 

 and the sediment content kept at I c.c. The sediment was then 

 stained and the cells counted in the usual manner. 



The Cellular Content in Relation to Certain other Factors. 

 The great irregularity of the cellular content of samples of milk 

 from apparently normal cows has been shown in the preceding 

 pages in connection with the methods of estimation. Some of 

 the variations may perhaps be due to experimental error, but it 

 is likely that there are normally very wide variations between the 

 cell content of different samples of milk. Several investigators 

 have endeavoured to ascertain the possible relationship between 

 the cell content and other factors, such as the stages of lactation 

 and an unhealthy condition of the gland, also minor factors, such 

 as fat content and reaction of the milk. 



Stages oj Lactation. There is some diversity of opinion as to 

 whether the cellular content is higher in colostrum than in later 

 milk. 



Gratz and Maray believe that there is frequently no increase 

 in leucocytes in colostral milk. 



Savage investigated a large number of samples of milk from 

 individual cows. In regard to the period of lactation he was unable 

 to trace any relationship with the leucocyte count, except in the 

 case of cows which were also pregnant, when the number of cells 

 tended to rise towards the end of lactation. The diminution of the 

 amount of milk given was found to be associated with a rise in the 

 number of leucocytes, and the less the amount of milk yielded, the 



