CHAPTER VI 



Experim^ital hiologt/. Prcfannation in a new dress, organ- 

 izaiimi of the egg, regeneration and gmfting, plastic 

 mrgery, tissue culture, the prahleni of death, and im- 

 mortality of the cell. 



The last thirty years have seen remarkable developments 

 in the field of experimental biology. True it is that the 

 method of experiment was a very early one, especially among 

 human and plant physiologists. Nevertheless experimental' 

 biolog\^ has lagged behind experimental physics and chem- 

 istry and has but recently found its proper place among the 

 other branches of biological science. In the development of 

 this field Germany and America have played the leading 

 part, while with the recent upheaval in Europe, and conse- 

 quent check to scientific progress there, the coming era of 

 reconstruction finds this country better fitted than any other 

 to lead in the development of the new science. 



"While the earlier biologists were in the main satisfied with 

 the observation of phenomena, and speculation as to their 

 causes, the experimental biologist demands that these pl^e- 

 nomena shall be analyzed under certain imposed conditions, 

 in order that their causes may be scientifically ascertained. 

 Thus the method of transmission of yellow fever could only 

 be conjectured until the Yellow Fever Commission in 1900, 

 by exposing subjects to all possible conditions of infection, 

 proved that the bite of the mosquito (Stegomyia) was the 

 only natural means of transfer. 



Experimental biology has followed a few main lines of 

 thought, with many side lines which are branched and in- 

 terwoven with one another in an intricate maze. A gen- 

 eral review may best be given by tracing the main lines, the 

 branches being folloAved only so far as they are essential to 

 an understanding of the former. The principal questions 

 then with which we shall deal are the following: 



Are the factors which determine the development of an 

 organism internal or external ? AYhy does an organism grow 

 old and die? What are the factors of organic evolution? 

 Is the organism a machine, governed by the laws of physics 

 and chemistry, or is there a "vital principle," an "en- 

 telechy" or a "soul," transcending in its activity the bounds 

 of the purely material universe? 



A century and a half ago Caspar Friedrich Wolff overthrew 



1 



