FKrvMENTATION. 263 



the bounds of surgery proper, and enter the domain of 

 epidemic disease, including those fevers so sagaciously 

 referred to by Boyle. The most striking analogy between 

 a contagi'iiin and a ferment is to be found in the power 

 of indefinite self-multiplication possessed and exercised 

 by both. You know the exquisitely truthful figures 

 regarding leaven employed in the New Testament. A 

 particle hid in three measures of meal leavens it all. A 

 little leaven leaveneth the whole lump. In a similar 

 manner, a particle of contagium spreads through the 

 human body and may be so multiplied as to strike down 

 whole populations. Consider the effect produced upon 

 the system by a microscopic quantity of the virus of 

 smallpox. That virus is, to all intents and purposes, 

 a seed. It is sown as yeast is sown, it grows and 

 multiplies as yeast grows and multiplies, and it always 

 reproduces itself. To Pasteur we are indebted for a 

 series of masterly researches, wherein he exposes the 

 looseness and general baselessness of prevalent notions 

 regarding the transmutation of one ferment into another. 

 He guards himself against saying it is impossible. The 

 true investigator is sparing in the use of this word, 

 though the use of it is unsparingly ascribed to him ; 

 but, as a matter of fact, Pasteur has never been able to 

 effect the alleged transmutation, while he has been 

 always able to point out the open doorways through 

 which the afErmers 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 



• Those who wish for an illustration of the care necessary in 

 these researches, and of tlie carelessness with which tliey have in 

 some cases been conducted, will do well to consult the Rev. W. H. 

 Dallinger's excellent ' Notes on Heterogenesis ' in the October 

 number of the Po£ula/r Science Review. 



