320 Dr Eschrkht's Inquiries concerning 



generally exploded," judiciously adds the following remark 

 (p. 71) : — " The argument against equivocal generation is, 

 however, merely analogical, and therefore can have but a 

 certain degree of strength to whatever extent it be carried ;" 

 and he no less judiciously finishes his exposition with these 

 words : — " Upon the whole, it will be prudent to regard this 

 as one of those mysteries which the present state of our know- 

 ledge does not enable us to explain, or even to comprehend." 

 How just this final remark has proved to be, will be shewn 

 hereafter. 



The cases which this learned physiologist regards the most 

 difficult to be accounted for, are the appearance of intestinal 

 worms, and, still more, that of the seminal animalculae. As to 

 the intestinal w^orms, he mentions the supposition that their 

 germs are contained in our food, and that they are conveyed 

 into the intestinal canal and developed there, as being the 

 situation specifically adapted for their subsistence. But if this 

 explanation of their appearance has been considered in any 

 degree satisfactory, it argues a very imperfect knowledge of 

 helminthology. 



The reason why the theory of equivocal generation obtained 

 no footing in England, although it possessed in Needham one 

 of its most ingenious authors, was, in a great measure, the au- 

 thority of Harvey, whose maxim, " omne vivum ex ovo," w-as 

 commonly understood as opposed to the theory of spontane- 

 ous generation. Still it is not less true that the maxim was 

 never advanced in this sense by its author. When Harvey, 

 in the 63d of his " Exercitationes de generatione,'* states, 

 *' omnia animalia eodem modo ab oviformi prasmordio gene- 

 rantur,"' he adds immediately, " oviformi, inquam, non quod 

 illud figuram ovi referat, sed quod constitutionem et naturam 

 ejus possideat," which is farther explained in the 62d Exerci- 

 tation in this manner : — " His (animalibus et stirpibus) autem 

 omnibus (sive sponte^ sive ex allis, sive in aliis vel parttbus vel 

 excrement is eorum putrescentibus oriantuj') id commune est, 

 ut ex principio aliquo, ad hoc idoneo, et ab efficiente interno 

 in eodem principio vigente, gignantur ; adeo ut omnibus vi- 

 ventibus primordium insit, ex quo et a quo proveniant." His 

 whole theory is very clearly expounded shortly afterwards in 



