METHODS OF TESTING DISINFECTANTS. 517 



FIG. 106. 



posed to the action of the agent used. When clumps 



of bacteria exist we are not always assured of this, for 



only those on the surface of the clump 



may be affected, while those in the 



centre of the mass may entirely escape, 



being protected by those surrounding 



them. These clumps and minute masses 



are especially liable to be present in 



fluid cultures and in suspensions of 



the bacteria, and must be eliminated 



before the test is begun, if this is to be 



made by mixing them with solutions 



of the agent to be tested. This is 



best accomplished in the following 



way : the organisms should be culti- 



vated in bouillon containing sand 



or finely divided particles of glass; 



after growing for a sufficient length of 



time they are then to be shaken thor- 



oughly, in order that all clumps may 



be mechanically broken up by the sand. 



The culture is then filtered through a 



tube containing closely packed glass 



wool. 



The filtration may be accomplished 

 without fear of contamination of the 

 culture by the employment of an 

 AHihintube, which is practically noth- 



ing more than a thick-walled test-tube tures on which dis * 



-, , . , , infectants are to be 



drawn out to a finer tube at its blunt tested. 

 end so as to convert it into a sort of 

 cylindrical funnel. The tube when finished and ready 

 for use has the appearance given in Fig. 106. 



23 



