24 AN INTRODUCTION TO ZOOLOGY 



exhausted, scientific biologists should hold fast to the working 

 program that has created the sciences of biology. The vitalistic 

 hypothesis may be held, and is held, as a matter of faith; but we 

 cannot call it science without misuse of the word" (20, p. 21). 

 A great many scientists have recently come forward to combat 

 the old idea of vitalism, and, though some of them have made 

 errors, their influence as a whole has been highly stimulating to 

 zoological thought. 



Until comparatively recent times it was believed that organic 

 compounds could be built up only by living substance. Even 

 such an able scientist as Liebig supposed that his beef extract 

 contained some vitalistic principle that was imparted to those 

 who ate it. His ideas were overthrown by a simple experiment. 

 Six puppies from the same litter were divided into two lots; 

 three were fed beef extract and the others were allowed to remain 

 without any food whatever. Those fed with the beef extract 

 died first, thus demonstrating that the extract was more a stimu- 

 lant than a food. The belief that organic compounds could 

 only come from living organisms was proven erroneous as early 

 as 1828, when Woehler made urea by a synthetic process in his 

 laboratory. It was to combat such mtalistic ideas that the 

 " mechanistic " theory first arose, and its adherents have met 

 with a considerable degree of success. Experiments from many 

 sources might be cited which support the mechanistic view, but 

 only a few selected instances can be given. 



Many organs will carry on their normal activities when removed 

 from an animal's body. A turtle's heart will remain alive and 

 beat for a couple of days if it is placed in a dish containing a 

 proper mixture of mineral salts in water. Furthermore, the rate 

 of the beats may be increased or decreased at the will of the experi- 

 menter by varying the proportionate amounts of the salts in 

 solution. 



Organs from one animal may be grafted upon another. There 

 is a gland, the thyroid, in the neck of human beings, which, when 

 diseased, causes a malady known as goiter. The removal of the 



