108 NATURAL SCIENCE. FEB., 
absolutely free from all matter derived from the body of the diseased 
animal; but with regard to all experiments on the subject, it is to be 
wished it could be more conclusively shown that a more subtle 
poison than the comparatively gross microbe may not be present. 
It is assumed that the quantity of anything existing besides the 
microbes in the original particles of injected matter would be so small 
that after a few generations nothing could remain; but in connection 
with this we have to remember the extraordinary divisibility of 
matter, and also that, conceivably, this other something may have 
the power of increasing as well as the microbe. 
Might it not possibly be that the action of the oxygen—which 
Pasteur thinks modifies the microbe—gradually destroys this other 
poison? and might not the phenomena of protective inoculation 
be an acclimatisation of the system to gtadually increasing doses of 
poison, akin to that by which a man can accustom himself to larger 
and larger doses of arsenic and opium? But this is the merest 
suggestion. 
It involves, moreover, the larger question of whether the experi- 
ments of Pasteur and others really necessitate the belief that the 
microbe is the sole and primary cause of the disease, and cannot be 
treated of here. 
The above remarks apply to attenuated viruses in which the 
microbe itself is supposed to be the active agent. But many recent 
investigators, instead of using an attenuated culture of the microbe 
for inoculation, inject small quantities of the toxic principle produced 
by its growth. -After the culture has proceeded to a certain extent, 
it is carefully sterilised, and the toxic principle is obtained free from 
microbes or their germs. To such methods of inoculation the 
exhaustion theory, of course, does not apply. 
It has even been shown, in the case of the bacillus of tetanus, 
that it is the toxic principle, and not the microbe, which causes the 
disease. Thus MM. Vaillard and Vincent? assert that if the inocu- 
lation be effected with a culture in which the bacillus has not had 
time to produce the toxic principle, or with a culture further advanced, 
but washed, so as to get rid of the poison, the symptoms of tetanus 
are not produced. On the other hand, a very small dose of the toxic 
principle does produce them. 
MM. Rodet and Courmont,* again, have shown that in the 
cultures of Staphylocoque pyozene there are two distinct principles, 
which can be separated by the action of alcohol. The one, insoluble’ 
in alcohol, has a prophylactic value; the other, soluble in alcohol, 
renders an animal more susceptible to the disease produced by the 
microbe. Thus, while animals inoculated with the former are more 
or less protected from the disease, those inoculated with the latter 
are rendered more susceptible to it. 
Comptes Rendus, vol. cxii., p. 239. % Comptes Rendus, vol. cxiii., p. 432. 
