INFECTIOUS DISEASES AND MICROBES, ETC. 189 



mic syringe (see Fig. 20), filled with the diluted dog- 

 virus, and inserts it under the dura mater, injecting 

 two drops of the virus. The disc of bone is then 

 replaced, and the skin flaps are sewed together by 

 means of two or three sutures. ' A pad of cotton 

 wadding, carefully purified by heat, is used to dry 

 the skin, after which a little of the same wadding is 

 used as a dressing ; this dressing is kept in position 

 by a free application of flexile collodin, the two 

 together forming an air-proof shield, through which 

 no microbes from the external air can make their 

 way to the wound, which, as a rule, heals up most 

 perfectly in less than a couple of days/ 



After death the brain and medulla oblongata are 

 removed, and a dilute virus is prepared from them, 

 as in the case of the dog-virus. This is injected 

 beneath the dura mater of a second rabbit, the 

 operation being repeated in fresh rabbits until the 

 shortest incubation period has been reached. This 

 incubation period of seven days' duration is reached 

 by the fiftieth passage, the rabbit taking ill on the 

 seventh day, and dying on the tenth day or later, is 

 the one used for human inoculations as well as for 

 the purpose of perpetuating the disease in other 

 rabbits. By dealing with a sufficiently large number 

 of animals it is possible to have a rabbit dying 

 every day, and thus also to put one spinal cord in a 

 desiccating bottle every day. By the fourteenth 

 day there will be a set of fourteen marrows under- 

 going the desiccation. These marrows vary in 

 virulence. The marrow of one day's desiccation is 

 the most virulent, and the virulence of the other 



