70 BIOLOGICAL LECTURES. 



with such conclusiveness as by Darwin, has been generally 

 adopted by naturalists of every nation. 



To accept Darwin is to accept the proposition that there 

 never was a first horse or first rose or first man. The 

 ancestry of the horse has been traced back through a long 

 series of forms as far as an extinct animal, known in zoology as 

 the paleotherium, which was no more like a modern horse than 

 is a tapir; but this distant animal may have been extinct for a 

 million years or more. No matter how long now, the point is 

 that the old notion has been given up, and appeal has been 

 'made for all changes in form, size, habits, and adaptations to 

 processes now going on, and all appeal to other or superphysical 

 agencies has been abandoned by naturalists of every country. 

 This means that in such important matters as the phenomena 

 of living things there is felt to be no necessity for going 

 beyond ordinary factors operating to-day, in precisely the same 

 sense as was the case of geology and astronomy. The expla- 

 nations accord with experience, and exposition is only the pre- 

 senting of factors and conditions in their proper order. The 

 explanations in each of these are adequate only when the ante- 

 cedents are sufficiently well known to make it plain they need 

 no supplementary, unrelated factors. 



We hear in these days of the forces of nature, of heat, of 

 light, of electricity, and the latter especially is popularly con- 

 sidered as a very mysterious something which nobody can 

 understand. These factors are supposed to act upon matter 

 and compel it to do this or that, go here and there. Heat in 

 the old books was often called caloric, and that was supposed 

 to be an imponderable something which could now be in matter 

 and now out. When in it, it caused the matter to exhibit 

 certain kinds of phenomena; when it was out, none inquired as 

 to where it was or what it was about. During this century it 

 has been conclusively proved that heat is but a particular kind 

 of motion. When one body strikes another body it imparts 

 some of its motion to it for mechanical reasons, and if a body 

 possessing heat motion comes in contact with another body 

 having less of that kind, it imparts some of that heat to it. 

 What one loses the other gains. There has been nothing 



