DELEPINE, BABCOCK, AND GERBER 181 



estimation of the sediment somewhat overlaps in that direc- 

 tion and its amount, " caeteris paribus," should bear some 

 relation to the number of cells and bacteria. 



The methods that have been proposed for the estimation of 

 the sediment in milk may be divided into two main groups. 



(1) Preparation of sediment by centrifugalisation. 



(2) Preparation of sediment by filtration. 



Group 1. One of the oldest methods of this type is that of 

 Houston 1^ who added 1 c.c. of formalin to 1 litre milk and 

 allowed the mixture to stand in a long tube with a narrow lower 

 graduated extremity closed by a glass tap. A primary reading 

 was obtained after tvv^enty-four hours by making a direct obser- 

 vation on the scale. The sediment was then flushed out into a 

 small graduated tube and the volume made up to 10 c.cms. with 

 slightly alkaline water (0.1 per cent Na2C03). After cen- 

 trifugaUsation for two minutes, a further observation was 

 made. This was termed the '' secondary reading." On 

 account of the large volume of milk required, this method has 

 not been generally adopted. 



Delepine, Babcock, and Gerber all adopted methods in 

 which the milk was centrifugalised for a specified time and the 

 volume of sediment read off directly on the graduated lower 

 extremity of the tube. Conn modified the usual centrifugal 

 method by washing the sediment with distilled water and, 

 finally, collecting it in tared filter papers which were after- 

 wards dried and weighed. To convert the dry weight to a 

 moist weight a factor was necessary and this was found to 

 average 7. This factor was somewhat variable and depended 

 upon the nature of the debris. Revis ^^ uses a tube having a 

 capacity of approximately 70 c.cms. ; to this is attached a small 

 glass cup by means of a ground-glass joint. Inside the con- 

 stricted lower portion of the larger tube a glass rod is ground in 

 to form a plunger valve. 



In the determination, the lower glass cap is fitted and 50 

 c.cms. of milk placed in the tube which is then whirled for five 

 minutes at 2000 revolutions per minute. After inserting the 



