154 THEORY AND PRACTICE 



truding the non-nutritious residue. A vegetable organism is 

 nourished through the cell wall, which encloses the protoplasm, 

 by organic or inorganic substances held in solution. This defi- 

 nition allows the vegetable organism both organic and inorganic 



food. 



The discovery of the various agents of contagious diseases has 

 produced the germ theory. This is as follows : 



When a specific germ of a specific disease is inoculated into a 

 healthy animal, it will produce that same specific disease and no 

 other. • The period of incubation is the time elapsing between the 

 inoculation and the first physical signs of the disease. This may 

 be called the incubative stage. 



VARIOLA. 



Variola is a specific disease affecting all higher animal life, but 

 each species of animal has its own kind of variola and this is 

 communicable to all other species. The human variola is the 

 small pox ; equine is the horse pox ; bovine, cow pox or vaccina ; 

 then we have goat pox, pig pox, chicken pox, etc., but every pox 

 is contagious. 



Course. — Variola runs through four definite stages; viz. 1. 

 Pimple ; 2. Vesicle ; 3. Pustule ; and 4. Scab. Prior to the phys- 

 ical manifestations of the pox, there is probably a little fever, es- 

 pecially in the lower animals. In the human the pox is fre- 

 quently fatal as is the case in black pox. In the lower animals 

 the pox is mild. This disease is non-recurrent ; one attack rend- 

 ers an animal permanently immune. Chicken pox may render 

 some little degree of immunity in the human, and cow pox most 

 certainly does. Vaccination is based upon the 



1. Intercommunicability of the disease. 



2. Non-recurrence of the disease. 



History of Vaccination. — Dr. Edward Jenner, an English 

 country practitioner, discovered the principles of vaccination. He 

 was the first to notice that the milkmaids did not take the small 

 pox, that the}^ were practically immune. In 1768 he discovered 

 the reason why. He examined cows and people and found that 

 the cows frequently had kine pox. He began inoculating people 



