122 PASTEUR AND AFTER PASTEUR 



periments : but the following examples will show 

 the lines on which the work was carried out : 



1. Two cages were placed in a glass box, inacces- 

 sible to fleas from outside. In cage A was put a 

 rat artificially infected with plague ; and from 10 to 

 20 rat-fleas were put with it. When the rat died, 

 a healthy rat was put in cage B. With healthy 

 rats, specially imported from England, and there- 

 fore above suspicion of previous exposure to plague, 

 11 out of 16, put in cage B, got plague. To 

 exclude the possibility of aerial infection, healthy 

 English rats were exposed not to plague-rats, but 

 only to fleas from plague-rats : and 8 out of 13 

 died. 



2. Small rooms were so constructed as to be " flea- 

 proof." All animals put in them were carefully 

 searched, to make sure that they had no fleas. 

 Fifty guinea-pigs were put in a flea-proof room, 

 7 feet by 6 feet, and ten artificially infected guinea- 

 pigs were put with them. The room was purposely 

 not cleaned out, so that, in a few days, the animals 

 were living in most insanitary conditions. As the 

 infected guinea-pigs died of plague, the bodies were 

 left for twenty-four hours before removal, so as to 

 afford every chance for contagion to play its part. 

 Yet not one of the fifty healthy animals died. 



3. Five infected guinea-pigs were put in a room, 

 died of plague, and were removed. Then twenty- 



