192 MILK AND THE PUBLIC HEALTH CHAP. 



constructed capillary pipette with a rubber bulb. The drop is 

 spread evenly over an area of 1 sq. c.m. on an ordinary 

 glass slide. The milk is then dried with gentle heat, the fat 

 dissolved out with xylol or other fat solvent, the smear fixed 

 to the slide by immersion in alcohol for a few minutes, dried, 

 overstained with methylene blue, and decolorized with 

 alcohol. The slide is then ready for examination. Eapid 

 drying is necessary to prevent the segregation of the fat drops 

 which makes the distribution of the cells uneven. 



The counting is done with an oil immersion lens. If the 

 diameter of the field is so arranged that it equals 0*16 m.m., 

 then each field covers approximately ! 005 of a sq. c.m. On 

 this basis each cell seen in a field taken at random represents 

 500,000 cells per c.c. The authors record that the cells are 

 evenly distributed. While an improvement on the original 

 smear method, many errors are obviously possible. 



To reliably estimate the cellular content of milk there are 

 only two methods (including later modifications of these 

 methods) with any pretensions to accuracy : the Doane-Buckley 

 method published in 1905, and the method of the writer, which 

 was independently worked out about the same time, but not 

 published until the following year. Both are based upon the 

 same principle, but show essential differences in technique. 

 By using as much as 10 c.c. of milk, the Doane-Buckley 

 counts are in the writer's opinion liable to be much too low. 



The German method of Trommsdorf consists in reading oft' 

 the volume of centrifugalised deposit in a drawn-out graduated 

 tube. The deposit consists of other matters besides leucocytes, 

 and cannot be taken as an estimation of their number. The 

 volume of total deposit does not bear any direct or constant 

 relationship to the leucocyte count. 



Savages Method. The ordinary Thoma-Zeiss blood- 

 counting chamber is employed. Direct counting of the cells 

 is impossible owing to the opacity caused by the large amount 

 of fat. One c.c. of the milk is accurately transferred to a cen- 

 trifugal tube (about 15 c.c. capacity) of the pattern shown in 

 Fig. 9, and freshly filtered Toisson's solution 1 is poured in to 



1 This is the well-known indifferent solution used in blood enumerations. 

 It does not injure the cells, but stains them sufficiently to render them clearly 

 visible. Its composition is methyl violet 0'025 grm., sodium chloride 1 grm., 

 sodium sulphate 8 grms., glycerine 30 c.c., distilled water 160 c.c. 



