280 PARASITIC BACTERIA 
were so weak as to be unable to produce a fatal disease, even in sus- 
ceptible animals. 
After reaching this result Pasteur, by an ever memorable 
experiment, demonstrated to the world the possibility of com- 
bating infectious diseases by the use of what are now known as 
weakened cultures. He inoculated half of a lot of fifty susceptible 
animals, including cattle and sheep, with his weakened virus. 
The animals were slightly indisposed, but suffered no evil con- 
sequences. In a few days he inoculated them with a second, 
stronger culture, with a like harmless result. Having thus 
prepared these test animals, he summoned to a public experi- 
ment an assemblage of noted men in Paris, and, in the presence of 
them all, inoculated the entire fifty animals with the strong 
infectious material taken from an animal dead from the disease. 
Two days later the company assembled again to find all of the 
unprotected animals either dead or dying from a violent case of 
anthrax, while of the protected animals not a single one showed 
the slightest evil result from the inoculation. 
A more beneficial discovery has hardly ever been made. From 
the date of Pasteur’s experiment a constant succession of bacteri- 
ologists has been trying to apply the same principle elsewhere. 
We cannot here attempt to follow the development of the work, 
but can only state that practical results of the utmost value have 
been obtained. It has not been found possible to use just the 
same method in other diseases that Pasteur used, but by a modi- 
fication of it, or by others that have come from it, it has been 
found possible to withdraw the terrors from some of the most 
dreaded diseases. The human diseases diphtheria, lock-jaw, 
bubonic plague, cholera, and hydrophobia have either been mastered 
or at least mitigated by discoveries that have come from the 
study which Pasteur started; while among animals at least two 
diseases are controlled by preventive inoculation—anihrax and 
black leg. Some success also has attended similar methods with 
tuberculosis. 
