IMMUNITY AND ANTITOXINS 



255 



ing of its virulence, just as certain other conditions increased 

 its virulence. Next he established the fact that subcutane- 

 ous injection of a weak virus, followed up with doses of 

 ever-increasingly virulent cords, immunised dogs against 

 infection or inoculation of fully virulent material. From 

 this he reasoned that if he could establish a standard of 

 weakened virulence he would have at hand the necessary 

 " vaccine " for the treatment of the disease. 



Subsequent research and skilled technique resulted in a 

 method of securing this standard, which he found to be a 

 spinal cord dried for fourteen 

 days. The exact details are as 

 follows: The spinal cords of two 

 rabbits dead of rabies are removed 

 from the spinal canal in their en- 

 tirety by means of snipping the 

 transverse processes of the ver- 

 tebrae. Each cord is divided into 

 three more or less equal pieces, 

 and each piece, being snared by a 

 thread of sterilised silk, is care- 

 fully suspended in a sterilised glass 

 jar. At the bottom of the jar 

 is a layer, about half an inch 

 deep, of sterilised calcium 

 chloride. The jars are then 

 removed to a dark chamber, 

 where they are placed at a 

 temperature of 20-22 C. in 

 wooden cases. Here they 



are left to dry. Above each case is a tube of broth, to 

 which has been added a small piece of the corresponding 

 cord, in order to test for any organismal element that may 

 by chance be included. In case of the slightest turbidity 

 in the broth, the cord is rejected. Fourteen series of cords 



SUSPENDED SPINAL CORD 



In drying jar containing Calcium Chloride 



