134 TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
of putrefactive and other changes, and the efforts of Lister 
to exclude those germs from wounds, and to render them in- 
nocuous, called attention to the subject in a marked manner. 
More recently the enquiries of Professor Koch into the bacillus — 
the so-called comma bacillus — of cholera, have given rise to a 
great deal of discussion ; it being argued by some that the 
bacillus found by Professor Koch is harmless, and is found 
naturally in the saliva. Doubtless in many cases the microbes 
are simply present, but are not the cause of the disease. The 
only way to ascertain this is by what is called cultivation. The 
suspected bacteria, micrococci, and the like, are cultivated in a 
suitable medium, proper precautions being taken to avoid the 
introduction of foreign germs. The experiment is then tried 
as to whether the cultivated germs will reproduce the disease 
when introduced into the system of an animal. By the so- 
called attenuation of these germs a milder form of the disease 
is produced, and so the system can be rendered proof against 
the specific disease of which the germs have been so treated. 
Thus with regard to the plan adopted by Pasteur to prevent 
anthrax — malignant carbuncle. The bacilli, or rod-like bodies 
of anthrax, sometimes contain spores, which have an extraordinary 
vitality, and are intensely virulent. 
Tyndall found that by a process of discontinuous heating he 
could kill them. The spores in the intervals between the 
heatings sprout into rods, and these perish at the next boiling 
before they have time to develop spores. After three or four 
heatings all vitality has been destroyed. 
Pasteur takes this microbe in the rod stage of its development, 
and keeps it in a temperature which favours its existence, and 
even its multiplication by division, but which is not sufficient 
to further favour the development of spores. At a temperature 
of 42° or 43° C. the microbe produces no spores. Therefore, in 
contact with pure air, he could maintain a culture deprived of 
all spores. In some weeks the crop dies; for being rendered 
sporeless by this enforced method of development, it is easily 
destroyed; but by favouring conditions it can be revived prior 
to its extinction. Then with this attenuated anthrax microbe 
Pasteur vaccinates sheep, horses, and oxen, and makes them proof 
against the disease itself. In. 1883 500,000 of these animals 
were vaccinated. 
