16 



PRINCIPLES OF ANIMAL BIOLOGY 



ieal work appreciably. The theoretical and natural history phases of 

 biology also went on quite unaffected, for the time, by cell discoveries. 



Modem Physiology. — Physiological investigations were much more 

 dependent upon the advances being made in animal chemistry than upon 

 cell studies. Knowledge of the composition of all sorts of animal struc- 

 tures was strengthening the belief that life is a group of chemical phe- 

 nomena. Studies of function necessarily made use of the experimental 

 method, which once more became one of the most valuable tools of 

 biology. One of the leaders of this period in physiology studied the 



Fro. 12. — Jean Baptiste Lamarck, 1744-1829. (From Locy, " Biolosjij and Its Makers" 



and Thornton, " British Plants." } 



processes of nutrition (particularly the role of the liver), the production 

 of sugar in animal bodies and the influence of the central nervous system 

 upon this process, the secretion of the pancreas, and the effects of poisons. 

 Another studicxl sense perception and the function of different kinds of 

 nerve cells, while a third worked on reflex actions. But all this was done 

 without particular reference to cells. It was t)nly much later that the 

 physiology of the cell was recognized as lying at the foundation of all 

 physiology. 



Evolution. — Another of the great developments of the nineteenth 

 century which occurred quite without reference to the knowledge of cells 

 was the growth of the evolution doctrine. The idea of evolution, or 

 change of species, was briefly and crudely stated or suggested in the writ- 

 ings of the early Greeks, Empedocles in particular. Linnaeus, in the 



