EXPRESSION OF RESULTS 177 



method but differing radically in technique. This was pub- 

 lished in 1906. 9 The method of Savage is the better one of 

 the volumetric methods, so full details will be given: 1 c.cm. 

 of milk is placed in a tube having a capacity of 15 c.cms. and 

 diluted with Toisson's solution (see Appendix) until the tube 

 is almost filled. The tube used is of special shape having the 

 lower end about one-quarter the diameter of the general body 

 of the tube and accurately graduated at 1 c.cm. After well 

 mixing the fluids, the tube is centrifugalised at 1800 revolu- 

 tions per minute for ten minutes. After breaking up the cream 

 with a clean rod the tube is whirled for a further five minutes. 

 The supernatant liquid is removed through a fine tube by 

 means of a vacuum pump until just 1 c.cm. remains. After 

 distributing the cells as evenly as possible in the sediment, a 

 sufficient quantity is placed in the cell of a Thoma-Zeiss or 

 some other convenient form of hsemocytometer and the cells 

 counted in a number of fields of vision. Savage recommends 

 drawing out the microscope tube until an exact number of 

 squares spans the field of vision and gives the following formula 

 for calculating the number of cells per cubic m.m. 



56,000?/ 

 cells per cubic m.m. of milk= 



where y = the average number of leucocytes per field of vision, 

 d = the number of squares which just spans the diameter. This 



56 000 

 approximation of jy - is accurate to within 0.5 per cent. 



The cells in the ruled squares can also be counted and the result 

 calculated as in ordinary blood work, but as these represent 

 but a small proportion of the total area of the cell, errors due 

 to unequal distribution of the cells would be proportionately 

 greater. 



Hewlett, Villar and Revis add 6 drops of formalin to 60-70 

 c.cms. of milk in order to break down aggregations of cells and 

 to prevent the cells being entangled in the cream layer. The 



