DEMONSTRATION OF "GENERAT1O .EQUIVOCA" 3 



However alluring a closer acquaintance with these minute creatures may 

 have been to the investigators who succeeded Plenciz, and however useful, 

 from a practical point of view, might be to observers the processes of de- 

 composition which they induced, these questions were nevertheless forced 

 temporarily into the background by another, namely, the origin of these 

 minute organisms. 



How do the minute creatures so copiously developed in infusions originate ? 



Some opined that these organisms were produced from certain unorganised 

 (and therefore inanimate) substances chemical compounds present in the 

 liquid in question, their formation being therefore considered as spontaneous 

 (generatio spontanea), or arising from elementary substances (primary genera- 

 tion). Or, whilst proceeding from elementary substances, as differing therefrom 

 (heterogeneous), or dissimilar thereto (equivocal) ; hence the name Heterogenesis 

 or generatio cequivoca : all of which terms, as well as that immediately to be 

 noted, have the same import. 



The party opposed denied, on the other hand, the possibility of a transition 

 from a lifeless to a living condition (abiogenesis), and asserted that when " infu- 

 soria" are detected in an infusion, a liquid or matter undergoing decomposition, 

 their existence is due to living germs present therein. 



Which view is correct ? On this point there arose, about the middle of the 

 eighteenth century, what formed one of the liveliest disputes agitating the 

 domain of natural science at that period, and which, after occupying the most 

 earnest attention of several successive generations of scientists, only terminated, 

 after numerous fluctuations, about the middle of the present century. From 

 among the numerous investigators who took part in this controversy, mention 

 can here be made of but few Needham 011 the one side and Spallanzani on the 

 other being entitled to the first place. 



3. Needham's Demonstration in Favour of 

 "Generatio Jquivoca." 



The most energetic champion of the theory of spontaneous generation was 

 the English divine, NEEDHAM (I.). This theory was in existence long before 

 his time, and had had renowned supportei-s among them the chemist Van 

 Helmont, who proposed a method for producing artificial mice but until then 

 had not progressed beyond the stage of indefinite assertion and unfounded 

 hypotheses. The cause of the extraordinary support and approval accorded 

 to the assumptions put forward by the English divine is, on the other hand, 

 attributable to the novel manner in which he arrived at his theory (pub- 

 lished in 1745), viz., not by untenable hypotheses, but by well-directed experi- 

 ments. 



He set to work, for example, in the following manner : An aqueous meat 

 extract was boiled for a short time in a flask, which was then made air-tight and 

 left to stand for several days or weeks. When opened at the end of this time, 

 the contents proved to be plentifully infested with "infusoria," from which 

 Needham concluded that as the "eggs" originally present in the liquid were 

 killed by the boiling and the entry of fresh ones from the outside was precluded, 

 therefore the living infusoria discovered in the liquid on re-opening the flask 

 must have originated spontaneously, not from eggs (germs), but from the lifeless 

 constituents of the liquid. 



The great impression produced on his contemporaries by these statements 

 can be appreciated by reference, for instance, to Buffon's work on the " System 

 of Generation." 



