VALUE OF VETERINARY SCIENCE. 209 



tagious. If the female moth was pounded up in a mortar 

 after death, and the debris examined microscopically, it 

 could be ascertained whether she was diseased or not. By 

 keeping each female with the eggs which she laid, he could 

 tell from the health of the moths whether her eggs were 

 healthy or not. If the moth was diseased, her eggs were 

 burned ; if she was healthy the eggs were allowed to hatch, 

 and thus a healthy supply of worms was assured. 



After completing his investigations of the silk-worm 

 trouble, he turned his attention to contagious animal dis- 

 eases, experimenting, at first, with anthrax and fowl cholera. 

 He found that these maladies were due to germs, which, in 

 certaia media, could be cultivated outside the animal body, 

 and when a creature was inoculated with a small quantity of 

 the artificially cultivated bacteria, the disease was reproduced. 

 He discovered, also, that in some instances the virility of 

 the bacteria was increased, and that, under other conditions, 

 it was decreased, and thus the disease could be induced in 

 a severer or milder form at will, and these experiments 

 finally led to one of the discoveries of the age, viz. : The 

 protective inoculation of animals or man against contagious 

 disorders, by means of the use of an attenuated virus. Bac- 

 teria, in order to live, require a certain amount of heat and 

 moisture, a suitable food, and either the presence or absence 

 of oxygen, and Pasteur discovered that, by growing them 

 at a greater heat than that of the temperature of the animals 

 they attacked, or by allowing them an abundance of air, or 

 by drying them, that their virulency might be decreased. 

 He has, also, found that the intensity of the virus of some 

 diseases can be increased by inoculating them upon certain 

 species of animals, and diminished by carrying a series of 

 inoculations through other species. For example, the viru- 

 lence of rabies is increased by inoculating rabbits from mad 

 dogs, and carrying the disease through a series of rabbits, 

 while by inoculating apes in the same way it was lessened. 



The idea occurred to Pasteur, that if an animal having 

 recovered from a contagious disease acquires immunity from 

 it, why should it not be possible to inoculate an animal with 

 an attenuated virus, which would not give the disorder, but 

 at the same time confer immunity upon it? His first attenu- 



