Summary 569 



innocuous in themselves, which attract a large number of leucocytes. I 

 In laboratory practice this method is in daily use for the purpose of 1 

 increasing the resistance of an animal against intraperitoneal injections 

 of various micro-organisms, and Durham has suggested the extension 

 of the same method to human medicine. Certain surgeons have 

 already made attempts in this direction. 



The application of the cellular theory of immunity to researches 

 on new micro-organisms of infective diseases has already been crowned 

 with success. Nocard and Roux have attempted to cultivate in the 

 animal body the virus of the pleuropneumonia of cattle. They selected 

 the rabbit, an animal naturally refractory against this infection. On 

 the supposition that, in this immunity, the phagocytes must play an 

 important part as destroyers of the presumed micro-organisms, the 

 idea suggested itself to them to withhold the virus from their voracity. 

 With this object they filled sacs of collodion or of reed pith with 

 pleuropneumonia virus, and introduced these sacs into the peritoneal 

 cavity of rabbits. Some time after this operation these investigators 

 were able to demonstrate in the contents of the sacs impregnated by 

 the blood fluid of rabbits, immune animals, the development of 

 specific micro-organisms, the smallest discovered up to the present. 

 By means of cultivations of this micro-organism, obtained in suitable 

 media, they worked out a method of vaccinating animals which, as 

 mentioned in Chapter xv., has already begun to give good results in 

 veterinary practice. This method has thus contributed to the pre- 

 vention of diseases, a branch of knowledge which has made such great 

 advances since medicine became an exact science under the inspiration 

 of the discoveries and ideas of Pasteur. 



Within a very short period immunity has been placed in possession 

 not only of a host of medical ideas of the highest importance, but also 

 of efiective means of combating a whole series of maladies of the most 

 formidable nature in man and the domestic animals. Science is far [594] 

 from having said its last word, but the advances already made are 

 amply sufficient to dispel pessimism in so far as this has been sug- 

 gested by the fear of diseases, and the feeling that we are powerless 

 to struggle against them. 



