GERMICIDAL POWDER OF CHEMICAL DISINFECTANTS 187 



TEMPERATURE OF EXPERIMENT 



It is a well-known principle in the use of disinfectants that, within certain 

 limits, the higher the temperature at which the disinfectant is used the greater 

 are its germicidal properties. This increase in the germicidal properties of dis- 

 infectants through the influence of heat is not the same for all disinfectants; 

 some, such as formaldehyde, are more strongly influenced than others. It will 

 be seen that at iSC. phenol, in dilution of i :8o, killed the typhoid organism 

 in 2^ minutes, while at a temperature of 3OC. the organism was killed in the 

 same length of time by a dilution of i : 120. 



On account of the great variation of temperature in the United States, espe- 

 cially during the summer' it becomes necessary that a standard temperature 

 be adopted. We have adopted a temperature of 2OC. and have devised a sim- 

 ple water bath to be used for maintaining this temperature. This bath consists 

 of a wooden box 20 inches deep, 21 inches long, and 21 inches wide. Inside this 

 box a i4-quart agateware pail 10 inches deep is placed and sawdust is well- 

 packed around, sufficient being placed on the bottom of the box to bring the 

 rim of the pail on a level with the top of the box. 



A tightly fitting wooden cover is placed over the pail, so made that the edges 

 project slightly over the rim. In the cover are a sufficient number of holes for 

 the seeding tubes, a thermometer, and the tube containing the culture. About 

 3 inches below the rim of the pail a false bottom of wire gauze is placed; this is 

 for the seeding tubes, etc., to rest on. Water is placed in the pail to within 

 }^ inch of the top. 



When an experiment is to be made the temperature of the water in the pail 

 is taken, and if above or below 2oC. it is brought to the desired temperature 

 by the addition of either cold or hot water. It will be found that only very 

 slight change takes place in the temperature of the bath in an hour and that it 

 is an easy matter to keep the temperature of the bath at the figures desired. 

 It is of advantage, in regulating the temperature of the bath, to have a spigot 

 in the bottom of the pail to draw off the water when so desired. 



PROPORTION OF CULTURE TO DISINFECTANT 



As disinfection is the result of chemical action of the disinfecting agent upon 

 the test organism, mass action is an important factor in the testing of disinfect- 

 ants. By this is meant that within certain limits the greater the number of 

 bacteria added to the disinfectant dilution the stronger the dilution required 

 to do the same work. For this reason it is important that the amount of culture 

 to be added to the dilution should be stated in definite quantities and not in 

 "drops" or in "spoonfuls." We have adopted the practice of using o.i cc. of 

 a 24-hour broth culture. For measuring this we use a delivery pipette gradu- 

 ated in tenths. 



