On Preventive Inoculation. 



'253 



amount of disappointment, as the application of the principle in a 

 number of instances did not give the expected results. 



Derivatives from Microbic Tims and their Effect. 



When we cultivate a pathogenic micro-organism in a liquid medium, 

 two different elements are obtained mixed together : the bodies of the 

 microbe and the liquid which it has modified, and into which it has 

 secreted its own products. 



A modification of the entire preparation, as represented by this 

 mixture, can be first of all obtained by filtering and separating the two 

 -elements just mentioned, and considering each of them by itself. 



Or else the two can be left together, and only the vitality of the 

 microbe destroyed by some physical or chemical agent. 



Or the constitution and the properties of each, or of both of these 

 elements can be, to a desired degree, altered by the admixture of 

 chemicals, or by subjecting them to physical processes. 



Or, the vital and pathogenic properties of the microbe can be mocli- 

 -fied by artificial breeding, and then the microbe itself, or the products 

 of such a modified microbe, used for treatment. 



The immediate effect which a given virus or its derivate produces 

 on an animal differs with the kind of virus taken, the process of 

 modification to which it has been subjected, and the species of animals 

 upon which it is used. The following instance may give an idea of 

 these variations. 



The ordinary Indian grey, as well as the brown, monkey are sus- 

 ceptible to the plague virus, and may contract a fatal disease from being 

 simply pricked with an infected needle. The rabbit and guinea-pig are 

 also susceptible to the disease. The horse, on the contrary, contracts 

 no fatal disease after being infected even with large doses of the 

 living virus. 



If, however, a plague culture be heated and the microbes killed in it, 

 the relative susceptibilities of the monkey and the horse seem to be 

 reversed, the guinea-pig remains comparable with the monkey, while 

 the susceptibility of the rabbit is now like that of the horse, and not, 

 as previously, like that of the monkey. 



It will require, according to several observers, a very large dose of 

 virus so treated to produce in the monkey or in the guinea-pig any 

 marked rise of temperature, or any alteration of the skin at the seat 

 of injection; while the horse answers to the injection by almost as brisk 

 an attack of fever as if the virus were a living one, and at the seat of 

 inoculation a tumour is produced which, if the dose be at all con- 

 siderable, may lead to a complete mortification of the tissue. The 

 Tabbit similarly answers to the injection by an attack of fever and by 

 the formation of a hard tumour at the seat of injection. 



As varied as is the immediate effect of different forms of virus upon 



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