294 FRAGMENTS OF SCIENCE 



'The great source of error here has been already al- 

 luded to in this discourse. The observers worked in an 

 atmosphere 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 differ- 

 ent 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 en- 

 abled 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 re- 

 searches the Bacterium remained a Bacterium, the Vibrio 

 a Yibrio, the Penicillium a Penicillium, and the Torula a 

 Torula. Sow any of these in a state of purity in an ap- 

 propriate liquid; you get it, and it alone, in the subse- 

 quent crop. In like manner, sow smallpox in the human 

 body, your crop is smallpox. 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 microscopic 

 organisms just enumerated do to their germs, or indeed as 



conducted, will do well to consult the Rev. "W. H. Dallinger's excellent "Notea 

 on Heterogenesis" in the October number of the "Popular Science E,eview." 



