THE FILTRATION OF COLLOIDAL SUBSTANCES 

 THROUGH BACTERIA-RETAINING FILTERS 1 



W. S. GOCHENOUR and HUBERT BUNYEA 



Bureau of Animal Industry, Department of Agriculture, Washington, D. C. 



Received for publication December 29, 1919 



It has been noted by the writers that in the preparation of 

 germ-free nitrates, notably in working with the anaerobic organ- 

 isms, those media which contained raw meat pieces added 

 aseptically were superior to media to which meat cubes were 

 added and which were subsequently sterilized by heat. It was 

 believed — a belief later confirmed — that the presence of the 

 unaltered proteins was chiefly responsible for the superiority 

 of those media of which they were an integral part. However, 

 the addition of meat cubes to previously sterilized media without 

 contamination thereof is difficult and unpractical on a large 

 scale. Therefore, in order to supply proteins unaltered by heat 

 the juice obtained by subjecting finely ground and previously 

 frozen and thawed raw meat was suggested as a substitute for 

 meat cubes in the expectation that this juice could be sterilized 

 by passing through a bacteria-retaining filter. 



Filtering of such a colloidal substance was found to be exceed- 

 ingly difficult. Inasmuch as no literature seemed to be available 

 which offered any assistance it is believed that a report of the 

 technique now used by the writers will prove helpful to others. 

 Preparation of the colloidal substances for the bacteria-retaining 

 filter by preliminary passage through cotton, asbestos wool and 

 filter paper does not appreciably enhance their filterability. 

 However, by adding a sufficient amount of pulverized kieselguhr 

 to the meat juice to make a very thin paste and pouring this 

 mixture over a coarse filter paper, the filtrate so obtained will 



1 Presented before Society of American Bacteriologists, December 29, 1919. 



363 



