HYDROPHOBIA. 327 



such as the sheep and the goat, the intravenous injection of 

 rabic virus, although it does not produce hydrophobia, 

 protects these animals against rabic infection. It is now 

 generally acknowledged that when properly performed, the 

 inoculation of even very large quantities of virus may be 

 safely carried out, and as it is found that greater success 

 is obtained where these larger quantities are injected we may 

 look forward to still greater improvement in the treatment of 

 this disease, and to even further diminished mortality. 



This process of inoculation in hydrophobia brings up a 

 phase of the vaccination question that has not yet been fully 

 developed but one that appears to be destined to cast an 

 important light on some of the questions relating to im- 

 munity. Pasteur's explanation of the results he obtained 

 does not appear to be entirely satisfactory. I am inclined 

 to think that the explanation advanced by Wood and myself, 

 that the treatment consists essentially in causing the tissues 

 to acquire a tolerance before the microbe has had time to 

 develop, is more in accordance with facts. The tissue cells 

 are acted upon by increasingly active virus, each step of 

 which acclimatizes the cells for the next stronger virus, until 

 at length when the virus formed by the micro-organisms 

 introduced at the time of the bite comes to exert its action, 

 the tissues have been so far altered or acclimatized that they 

 can continue their work undisturbed in its presence ; and 

 treating the micro-organisms themselves as foreign bodies, 

 destroy them. When the cells are suddenly attacked by a 

 strong dose of the poison of this virus they are so paralyzed 

 that the micro-organisms can continue to carry on their 

 poison-manufacturing process without let or hindrance, but 

 when the cells are gradually, though rapidly, accustomed to 

 the presence of the poison by the exhibition of constantly 

 increasing doses they can carry on their scavenging work 

 even in its presence, and the micro-organisms are destroyed, 

 possibly even before they can exert their full poison manu- 

 facturing powers. Some such explanation as this would 

 account for the interference with the course of the disease 

 even after the patient has been bitten. The micro-organism 

 is localized, it takes some time to form its poisonous products, 

 and whilst this is going on the whole of the nervous and other 

 tissues are being gradually acclimatized by the direct applica- 

 tion of small quantities of the poison artificially introduced. 



