IQ4 MEDICAL BACTERIOLOGY 



SEEDING TUBES 



The seeding tubes are glass test-tubes i inch in diameter and about 3 inches 

 long, with round bottoms. In order to measure the disinfectant into them they 

 are placed in a suitable wooden stand to receive them. We found it convenient 

 to use a wooden block containing six rows of 15 holes each for the disinfectant 

 to be tested and a separate stand for the phenol controls. The tubes are 

 placed in the stand and each marked with the strength of dilution it is to 

 contain. 



Starting with the lowest dilution (i.e., the strongest), the cylinder is shaken, 

 then 5 cc. are measured into the tubes marked 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 dilution, first blowing out as much of the re- 

 maining liquid as possible; then drawhig a pipetteful of the next dilution to be 

 used and discarding that; then filling the pipette a second time, which is emptied 

 into the seeding 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 standard temperature. We have not found it necessary to use cotton 

 plugs in the seeding tubes. They are sterilized in paper-lined wire baskets, 

 with the closed end of the tubes up. 



SUBCULTURE TUBE RACKS 



Wooden racks, with five rows of 14 holes each, are used for holding the sub- 

 culture tubes, and as plants are made from each mixture of culture and disin- 

 fectant every 2^ minutes up to 15 minutes, six tubes are required for each 

 dilution. Thus, in each rack we have ten rows of six tubes each with two 

 empty cross rows of holes remaining, which are utilized by placing over in the 

 next row each tube as it is planted. This makes it easy to keep run of the tubes 

 that are planted. It is well also always to plant from the seeding tube in a 

 certain hole in the water bath into a certain row of tubes in the rack. This, 

 after a little practice, will help to avoid errors in planting. 



METHOD OF CONDUCTING THE TEST 



If there are in one experiment more than 10 dilutions of the disinfectant, 

 including the phenol controls, the stronger solutions of the disinfectant and 

 phenol are tested first, as it will not be necessary to plant them after 7^ min- 

 utes. The weaker solutions are then immediately done and are then planted 

 every 2% minutes for 15 minutes. 



For keeping the time a stop-watch can be used, but an ordinary watch will 

 serve the same purpose by simply starting on the 2^- or 5-minute periods. 



