GEEMS OF DISEASE AND DEATH. 251 



take the case of small-pox, and its analogous condition 

 the fever produced by vaccination. When an infant is 

 vaccinated, the physician introduces into its system, 

 through an abrasion of its skin, a minute quantity of 

 vaccine lymph, which, as everybody knows, is obtained 

 either from the vaccination pustule of an already 

 vaccinated child, or direct from the calf. In either 

 case, there are introduced into the infant body, certain 

 minute germs suspended in and living naturally 

 amongst the vaccine lymph and in due course these 

 germs multiply and increase within the frame, thereby 

 producing the characteristic fever, and the equally 

 characteristic pustule at the seat of the operation. 

 So, also, with small-pox, which vaccination imitates in 

 a mild way, and of which, moreover, it is a preventive. 

 Here the germs of small-pox, obtained directly or 

 indirectly from an already infected person, attack the 

 body. Gaining admittance thereto, they propagate 

 themselves within the tissues and through the medium 

 of the blood. Sooner or later all the characteristic 

 symptoms of the disease are manifested, and having 

 run its course, it dies away as mysteriously, to all 

 appearance, as it came. Now, there is something 

 strikingly analogous in all this to the growth of an 

 animal or plant. There is a period of " incubation " 

 in the fever, just as in the production of the living 

 being there is a period of development. There is a 

 growth of the fever, as the animal or plant grows 

 towards its maturity ; and there is a decline of the 

 disease, as the living form passes to its old age and 



