110 THE CONCEPTION OF LIFE 



pied with so transforming their Tundamental conceptions 

 that they will correspond to the discoveries of recent years. 

 Some surprises will surely come in biology, and therefore I 

 prefer to take an agnostic position in regard to the doctrine of 

 spontaneous generation, and to cling to the possibility that the 

 final explanation will be found in some unexpected direction, 

 or will be given by some phenomenon as yet wholly unknown 

 to us. It is much achieved that we can now maintain the 

 statement that protoplasm, under which term we include the 

 nucleus, is the physical basis of life. 



Let us now pass to the consideration of the general activity 

 of protoplasm. First of all, we must regard metabolism which 

 we must look upon as the basic phenomenon of life. Very 

 many chemical substances are taken up by protoplasm which 

 in part are worked over into new chemical combinations, by 

 which the growth of the living substance is made possible, and 

 at the same time the necessary material is produced for the 

 performance of work. In consequence of the performance of 

 work simple chemical compounds arise which cannot be fur- 

 ther used by the protoplasm, and are therefore discarded, and 

 are designated by us as excretes. In order to maintain life, 

 the stream of matter through the protoplasm must continue. 

 We have no occasion to assume that metabolism is more than 

 a series of chemical processes. 



By nourishing itself, protoplasm grows, and as a conse- 

 quence thereof follows the multiplication or proliferation of 

 cells. We know also that when protoplasm grows, the new 

 formed protoplasm is similar to that already present. The 

 self-maintenance of its own peculiarities is highly character- 

 istic of protoplasm and we recognize in this peculiarity the 

 basis of heredity. The question of variations is a very differ- 

 ent one. The doctrine of evolution forces us to the assump- 



