518 BACTERIOLOGY. 



at the ordinary temperature. The drying- may be hastened 

 by placing 1 the dishes, slightly uncovered, in an incubator 

 at 37 for three hours. 



When the temperature of the oven has reached the de- 

 sired point, the proper number of silk threads, muslin 

 squares or cover-glasses are placed in a sterile Petri dish 

 which is then set within the oven on a level with the bulb 

 of the thermometer. At the end of stated intervals a silk 

 Thread, muslin square or cover-glass, is taken out as rapidly 

 as possible, by means of sterile forceps, and is transferred 

 to a tube of nutrient bouillon. This is labelled at once, and, 

 eventually the entire set is placed in the incubator. 



With infected silk threads, prepared as above, the student should 

 test the action of dry-heat on the several organisms already studied. 

 The results obtained in this, and in all other laboratory work, should 

 be arranged in tabular form to facilitate comparison and review of 

 results. 



Action of dry heat at 70. The silk threads should be withdrawn at 

 the end of 15, 30, 45 and 60 minutes' exposure. 



Action of dry heat at 100. The specimens should be withdrawn at 

 intervals as just given. 



Action of dry heat at 120. The specimens should be withdrawn at 

 same intervals as above. 



Action of dry heat at 150. The specimens should be withdrawn at 

 intervals of 5, 10, 15, 30, 45 and 60 minutes. 



Testing of Disinfectants. 



In studying the action of physical and chemical ag-ents 

 on bacteria it is necessary to rigidly adhere to certain re- 

 quirements without which the results would be of little 

 value, if not wholly contradictory. The conditions which 

 underly the testing- of disinfectants may be summed up as 

 follows : 



