170 LABORATORY METHODS OF 



the tubes and inoculate a new tube with the contents 

 of the hot tube ; wait a while and take out another tube 

 and proceed as in the above case, and so on, until you 

 have taken out several tubes, all at a different tem- 

 perature. Set the whole aside until the next period 

 and note which one has the growth on it. It will usual- 

 ly be the one that stays in the bath the shortest time 

 which will give the growth. The ones on which there 

 is no growth are dead and the temperature at which 

 they died is known by the reading on your tube, since 

 you noted the temperature when you took out each 

 eye of bouillon to inoculate the new tube. 



DETERMINE THE STRENGTH OF ANTISEPTICS AND GER- 

 MICIDES. 



Take some of the culture and subject it to the action 

 of different strengths of the germicides in a Petri dish 

 Any germ will serve for the test, or if the agent is a 

 gas, we will place some pieces of blotting paper, which 

 have been soaked in some good medium, and scatter 

 them in a closed chamber and set the gas generator 

 going. After a while take some of the paper and 

 smear the surface of a sterile medium and the growth 

 will not take place if the germicide is strong enough. 



INOCULATING ANIMALS. 



The mouse, guinea pig, rabbit, and white rat are the 

 ones that are used most. Take the animal and sterilise 



