FKRMKtfTATION. 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 m, 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 small-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 contagiurn 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 Ileview. 



