LABORATORY RESEARCH, ETO. 269 
Attenuation of Pathogenic Microbes.—Successive 
cultures have established, as we have seen, the pos- 
sibility of attenuating virus, and transforming it into 
vaccine. The processes employed to attain this object 
are complex and varied, according to the species of 
bacterium with which we have to do. 
Thus, for fowl-cholera, Pasteur found that cultures 
dating from fifteen days, or from one, two, eight, and 
ten months, progressively lost their virulence, and he 
believes this attenuation to be due to the action of the 
oxygen of the air. So, again, Koch supposes that the 
action of the air and the desiccation of the germs 
produces, after a time, the natural extinction of the 
disease. 
Toussiant and Chauveau attenuate the virus of 
anthrax, as we have seen, by subjecting it to a tem- 
perature of from 42° to 43°. Pasteur and Thuillier have 
attenuated the virus of swine fever by passing it 
through the system of a rabbit. Pasteur has also 
attenuated the virus of rabies, of which the microbe 
is still unknown, by passing it successively through 
the systems of a rabbit, monkey, ete. 
Finally, the same result may be obtained by add- 
ing various antiseptic substances to culture liquids, 
and thus weakening the virulent action of the 
microbe. 
Vaccination and Inoculation—The attenuated 
virus or vaccine thus obtained may be used for inocu- 
lation in quantities which experience indicates to 
