278 FEAGMENTS OF SCIENCE. 



alluded to in this discourse. The observers worked yi 

 an atmosphere charged with the germs of different 

 organisms ; the mere accident of first possession ren- 

 dering 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 or- 

 ganisms. 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 Bac- 

 terium, the Vibrio a Vibrio, the Penicillium a Penicil- 

 lium, 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 constant a relation to 

 its contagium as the microscopic organisms just enume- 

 rated 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 grow- 

 ing daily in strength, that reproductive parasitic life ia 

 at the root of epidemic disease that living ferments 

 finding lodgment in the body increase there and multi- 



