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, it 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 



