EXPERIMENTS. 667 



brush, rinse in hot water, then soak the hands for five 

 minutes in 1 : 1000 corrosive sublimate solution, and, 

 as before, prepare plates from scrapings from the same 

 localities. Note the results. 



Repeat this latter procedure in exactly the same way, 

 but before taking the scrapings let some one pour am- 

 monium sulphide over the points from which the scrap- 

 ings are to be made. After it has been on the hands 

 about three minutes again scrape, and note the result 

 upon plates made from the scrapings. 



Wash as before in hot water and soap, rinse in clean 

 hot water, immerse for a minute or two in alcohol, 

 after this in 1 : 1000 sublimate solution, and finally in 

 ammonium sulphide, and then prepare plates from 

 scrapings from the points mentioned. 



In what way do the results of these experiments 

 differ from one another? 



To what are these differences due ? 



What have these experiments taught? 



In making the above experiments it must be remem- 

 bered that the strictest care is necessary in order to 

 prevent the access of germs from without into our 

 media. The hand upon which the experiment is being 

 performed must be held away from the body and must 

 not touch any object not concerned in the experiment. 

 The scraping should be done with the point of a knife 

 that has been sterilized in a flame and allowed to cool. 

 The scrapings may be transferred directly from the 

 knife-point to the gelatin by means of a sterilized plat- 

 inum wire loop. 



The brush used should be thoroughly cleansed and 

 always kept in 1 : 1000 solution of corrosive sublimate. 

 It should be washed in hot water before using. 



