FERMENTATION. 553 
of such transmutations had allowed error to march in upon 
them.* 
The great source of error here has been already alluded 
to in this discourse. The observers worked in an atmos- 
phere charged with the germs of different organisms; the 
mere accident of first possession rendering now one 
organism, now another, triumphant. In different stages, 
moreover, of its fermentative or putrefactive changes, 
the same infusion may so alter as to be successively taken 
possession of by different organisms. Such cases have 
been adduced to show that the earlier organisms must 
have been transformed into the later ones, whereas they 
are simply cases in which different germs, because of 
changes in the infusion, render themselves valid at different 
times. 
By teaching us how to cultivate each ferment in its 
purity in other words, by teaching us how to rear the 
individual organism apart from all others Pasteur has 
enabled us to avoid all these errors. And where this isola- 
tion of a particular organism has been duly effected it 
grows and multiplies indefinitely, but no change of it into 
another organism is ever observed. In Pasteur's researches 
the Bacterium remained a Bacterium, the Vibrio a Vibrio, 
the Penicilliurn a Penicillin rn, and the Torula a Torula. 
Sow any of these in a state of purity in an appropriate 
liquid; you get it, and it alone, in the subsequent crop. 
In like manner, sow small-pox in the human body, your 
crop is srnall-pox. Sow there scarlatina, and your crop is 
scarlatina. Sow typhoid virus, your crop is typhoid 
cholera, your crop is cholera. The disease bears as con- 
stant a relation to its contagium as the microscopic organ- 
isms just enumerated do to their germs, or indeed as a 
thistle does to its seed. No wonder then, with analogies 
so obvious and so striking, that the conviction is spreading 
and growing daily in strength, that reproductive parasitic 
life is at the root of epidemic disease that living ferments 
finding lodgment in the body increase there and multiply, 
directly ruining the tissue on which they subsist, or de- 
* Those who wish for an illustration of the care necessary in these 
researches, and of the carelessness with which they have in some 
cases been conducted, will do well to consult the Rev. W. H. Dallin- 
ger's excellent " Notes on Heterogenesis " in the October number of 
the Popular Science Review. 
