4.26 FUNCTIONS OF THE NERVES. [ch. hi. 



repairing our bodies? Wonderful, indeed, is that property 

 whereby the adaptation of nutrient material to each portion of 

 the body is effected. This is done with such skill and wisdom, 

 that suitable and analogous particles are applied to every 

 part, and thus neither the composition nor character of their 

 constituent particles, nor the form or structure of the nourished 

 parts themselves, are disturbed by the continuous apposition of 

 new molecules. Particles which are adapted to the composition 

 of muscles or cartilage, are not deposited in bones, otherwise 

 bones would gradually lose their proper character, and become 

 cartilaginous or muscular. For these reasons, Blumenbach 

 correctly maintains,^ that generation, nutrition, and reproduc- 

 tion are effects or modifications of one and the same force, 

 which forms in the first, maintains in the second, and restores 

 in the third. ^ 



' Von dem Bildungstriebe, ^ 7. Gottingen, 1781. 



2 This expression, that the foetus is formed by generation, and not evolved from a 

 germ created from the beginning of the world, should not appear to the indulgent 

 reader altogether new ; for Casper F. Wolff has long ago much weakened the system 

 of evolutions set up by Bonnet and Haller, and established in its place the doctrine 

 of epigenesis of the ancients. Haller, it is true, continued to maintain his views in 

 his * Element. Physiol.,' tom. viii ; but after having carefully weighed his arguments, 

 I do not think them sufficient to estabUsh the doctrine of evolution, and confute that 

 of epigenesis. Hybrid animals, malformations of the parent transmitted to the off- 

 spring, the reproduction of whole structures, especially of certain animals, as well as 

 the generation of polypes and certain vegetables by cuttings, all confute the doctrine 

 of evolution, and prove that those germs in which, from all time, entire animals or 

 parts of them are marked out, do not exist; but that there must be some vis 

 structrix, which constructs the bodies of animals, however complicated, from suit- 

 able materials that it has ready at hand. I have treated of this more fully in my 

 dissertation on the system of generation, inserted in the Second Fasciculus of my 

 * Adnotationes Acaderaicae' for 1781. In the same year in which my dissertation 

 appeared, that elegant tract by Blumenbach, Professor at Gottingen, was published, 

 in which this vis structrix, or nisus formativus, as he terms it, is proved to exist, 

 and the doctrine of evolution by germs is rejected. This essay gives the greater 

 support to the doctrine of epigenesis, because the distinguished author himself 

 brought forward much in favour of the hypothesis of evolution in his work ' De Generis 

 Humani Varietate Nativa,' (Gotting., 1776 ;) but now, having had an opportunity of 

 observing the phenomena of reproduction in polypes, and feeling the weight of the 

 arguments in favour of epigenesis, has adopted it in place of the system of evolution. 

 He maintains that in every animal and vegetable organism, there is intimately 

 connected with it, during its whole life, a certain innate and ever-acting instinct, 

 which he terms the nisus formativus, in virtue of which animals and vegetables at- 

 tain their proper and fixed form ; when this is attained, the same force maintains it ; 



