THE MICROBES OF HUMAN DISEASES. 239 
poisonous substances greatly resembling vegetable 
alkaloids, and termed by them ptomaines. 
The action of ptomaines may be compared to that 
of strychnine. Injected into the blood, even after 
the removal of every living microbe, the ptomaines 
produce fever, rigors, vomiting, diarrhoea, spasms, 
torpor, collapse, and finally death. It is probable that 
in some cases of poisoning by tainted meat or fish 
their poisonous properties are due to the presence of 
ptomaines. i 
But in all cases these ptomaines are shown to be 
the product of putrid fermentation, which is always 
effected in dead bodies by special microbes. Here the 
ptomaines are due to the work of the microbes of 
putrefaction, and are made by them, just as alcohol 
and the carbonic acid of alcoholic fermentation are 
made by yeast, at the expense of the sugared liquid 
in which they live and multiply. 
Direct experiments show that when septine, from 
which every microbe has been removed, is injected 
into the human subject, it produces feverish disturb- 
ance, but only causes death when introduced in con- 
siderable quantities. If, on the other hand, there is 
in the same individual a large suppurating wound, 
exposed to the air instead of being covered by an air- 
tight dressing, a purulent infection (septicemia) will 
almost certainly ensue, since the microbes introduced 
by means of this wound will find in it a favourable 
soil (pus and putrefying organic matter); they will 
