STANDARDIZATION OF DISINFECTANTS 



239 



ning crosswise represent the same strength dilution, while the rows 

 running lengthwise represent the different strengths to be used in 

 the experiment. 



Starting with the lowest 

 dilution {i.e., the strongest), 

 the cyKnder is shaken, then 5 

 cc. are measured into the 

 tubes of the row to receive 

 that strength, using a 5 cc. 

 delivery pipette. In order to 

 economize glassware, the 

 same pipette is used for 

 measuring out the next dilu- 

 tion, first blowing out as 

 much of the remaining liquid 

 as possible, then drawing a 

 pipette full of the next dilu- 

 tion to be used and discard- 

 ing that, then filling the 

 pipette a second time, which 

 is then emptied into the seed- 

 ing tube. 



The measuring out being 

 completed, the tubes are 

 placed in the water bath and 

 allowed to stand a few minutes 

 in order that the disinfectant 

 solution may reach the stand- 

 ard temperature. We have 

 not found it necessary to use 

 cotton plugs in the seeding 

 tubes. They are sterilized in paper-lined wired baskets, with the 

 closed end of the tubes up. 



Subculture Tube Racks. — Wooden racks, with five rows of 



LH WILDER 



Fig. 85. — Water bath showing position 

 of holes for the thermometer and the seeding 

 tubes. — f^Anierson &" McC Untie, Hygiene 

 Laboratory Bulletin No 82, U. S. Public 

 Health Service.) 



