Testing Germicidal Value of Liquids 



257 



For the " subculture" tubes, any test-tube rack will do, but it 

 is more convenient to have a special rack or stand made. That 

 recommended contains five rows of 14 holes each. Each tube of 

 culture-medium is carefully marked with a blue pencil to show three 

 things, i, the germicide; 2, the dilution; 3, the time of exposure, and 

 stood in its place in the rack as will be explained below. 



Fig. 90. Block for subculture tubes (Anderson and McClintic, in Bulletin 

 No. 82, Hygienic Laboratory). 



Fig. 91. Device for flaming inoculating loops (Anderson and McClintic, 

 in Bulletin No. 82, Hygienic Laboratory). 



The transplantations from the seeding tubes to the culture tubes 

 are to be made every 2% minutes up to 15 minutes, so that for each 

 strength of dilution to be tested, there will be six tubes. In addition 

 to these test-tubes there will be four dilutions of phenol to act as 

 controls so that every 2% minutes ten transplantations must be 

 made. As 2% minutes contain 150 seconds, and as the picking up 

 and opening of the subculture tube, the transfer of the seed-culture 

 to the medium, the replacement of the stopper and the return of the 

 tube to the rack require about 15 seconds at the hands of an 



