148 THE POPULAR SCIENCE MONTHLY. 



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 isolation 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 Penicillium a Peni- 

 cillium, and the Torula a Torula. Sow any of these in a state of pu- 

 rity in an appropriate liquid, you get it, and it alone, in the subse- 

 quent 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 constant a relation to its contagium as the mi- 

 croscopic organisms 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 dis- 

 ease that living ferments finding lodgment in the body increase thei*e 

 and multiply, directly ruining the tissue on which they subsist, or 

 destroying life indirectly by the generation of poisonous compounds 

 within the body. This conclusion, which comes to us with a presump- 

 tion almost amounting to demonstration, is clinched by the fact that 

 virulently-infective diseases have been discovered with which living 

 organisms are as closely and as indissolubly associated as the growth 

 of Torula is with the fermentation of beer. 



And here, if you will permit me, I would utter a word of warning 

 to Avell-meaning people. We have now reached a phase of this ques- 

 tion when it is of the very last importance that light should once for 

 all be thrown upon the manner in which contagious and infectious 

 diseases take root and spread. To this end the action of various 

 ferments upon the organs and tissues of the living body must be 

 studied; the habitat of each special organism concerned in the pro- 

 duction of each specific disease must be determined, and the mode 

 by which its germs are spread abroad as sources of further infection. 

 It is only by such rigidly accurate inquiries that we can obtain final 

 and complete mastery over these destroyers. Hence, while abhor- 

 ring cruelty of all kinds, while shrinking sympathetically from all 

 animal suffering suffering which my own pursuits never call upon 

 me to inflict an unbiased survey of the field of research now open- 



