476 BACTERIOLOGY. 



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 results 

 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 am- 

 monium sulphide, and then prepare plates from scrapings 

 from the points mentioned. 



In what way do the results of these experiments 

 differ one from 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 pre- 

 vent 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 scrap- 

 ing should be done with the point of a knife that has 

 been sterilized in the flame and allowed to cool. The 

 scrapings may be transferred directly from the knife- 

 point to the gelatin by means of a sterilized platinum 

 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. 



