298 MICROBES, FERMENTS, AND MOULDS. 
since it is known that they elaborate, at the expense 
of the organism, a violent poison (ptomaine), which 
penetrates wherever the bacteridia cannot find their 
way. It can hardly be said that in this case the 
bacteridia are only a “secondary phenomenon ;” that 
is, an unimportant complication which gives no cause 
for uneasiness. 
What we have here said of anthrax also applies 
to other diseases: to diphtheria, small-pox, and inter- 
mittent fever. We venture to say that if our instru- 
ments were not sufficiently powerful to enable us to 
see the organisms which cause these diseases, reason 
alone would oblige us to admit their existence, from 
our general knowledge of the cause and nature of 
contagious diseases. The word “contagion” implies 
microbe, and the simplicity of the theory gives it 
value, and permits us to regard it as the expression 
of actual facts. 
After this, ib is unimportant to know whether the 
microbe is itself the contagion, or only its vehicle; if 
it acts by itself, or only by the production of ptomaine; 
if there is a specific microbe for each kind of disease, 
or if this microbe is susceptible of transformation, like 
other living things, according to the nature of the 
medium in which it is nourished. These are secondary 
questions, of which the future will doubtless afford the 
solution, but Which do not affect the principle of the 
parasitic theory. That theory is only just established ; 
each day brings a fresh stone to the edifice, but we 
