METHODS OF TESTING DISINFECTANTS 469 



PIG. 98. 



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 it 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 

 Allihin tube, which is practically noth- cylindrical funnel 



used for filtering cul- 



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



drawn out to a finer tube at its blunt j nf f<f nts are to be 



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. 98. 



21 



