THE CELLULAR CONTENT OF MILK 137 



tent to that attending the presence of inflammatory or other 

 diseased condition of the gland. This at once leads to a considera- 

 tion of the methods which have been employed for enumerating the 

 total number of cells present in milk. 



On the Methods of Estimating the Cellular Content of Milk. 

 It is evidently important that the method of estimating the cell 

 content of milk should be accurate if deductions are to be drawn 

 from the number of cells found. The difficulties met with are, 

 however, considerable, and preliminary manipulations are necessary 

 before the number of cells present can be estimated. 



Stokes (1897) was the first investigator to deal with a method 

 of estimating the cells in milk. His method consisted in 

 centrifuging 10 c.c. of milk for ten minutes in a tube. He then 

 removed the fat and supernatant liquid and examined a loopful of 

 the sediment spread over an area of I sq. cm. on a glass cover slip. 

 The film thus made was stained with methylene blue and ex- 

 amined with an oil immersion lens. The cells in ten fields were 

 counted and the average count per field obtained. When the 

 number of leucocytes exceeded ten per field, it was customary to 

 regard the milk as containing an abnormal number of cells and as 

 unfit for use. It is now generally admitted that this method of 

 Stokes cannot be regarded as sufficiently accurate. 



Stewart (1905) introduced a modification of this method. 

 He used i c.c. of milk in a small glass tube, of which the lower end 

 was closed with a rubber plug. The tube was then centrifuged 

 for ten minutes and the rubber plug carefully drawn out from the 

 tube, the sediment upon it being smeared over an area of I sq. 

 cm. on a cover slip. This was then stained and the number of 

 cells found in ten fields counted. As a result of practice it was 

 customary to regard the number as excessive when the count 

 exceeded twenty-three cells per field. 



Doane and Buckley introduced another method. This con- 

 sisted in taking 10 c.c. of milk in a glass tube which was marked 

 off in cubic centimetres. After centrifuging for ten minutes, the 

 fat and supernatant liquid down to the I c.c. mark were removed. 

 Stain was then applied to this remaining cubic centimetre and 

 a drop of the mixture placed in a Thoma-Zeiss apparatus and 

 the number of leucocytes per c.c. determined. Using this method, 

 it was estimated that cells were present in excess when the figure for 

 those counted showed a rate of more than 500,000 per c.c. of milk. 



A different form of test was introduced by Trommsdorff in 

 1906. This method does not involve microscopical examination. 

 Trommsdorff prepared small centrifuge tubes of which the lower 

 end was drawn out into the form of a capillary tube and graduated. 

 The graduations were arranged to show the volumes of sediment 

 per litre. He usually took 5 c.c. of milk, or for a general test 10 

 c.c. might be utilised. When, after centrifuging, more than one 

 volume per litre of sediment was found, suspicion of excess of 



