The monistic theory. 4I 



vanishes with its individual aspect; its features can 

 no longer be distinguished. 



Besides, a whole school of contemporary physicists 

 (Ostwald of Leipzig, Mach of Vienna) is beginning to 

 cast some doubt on the utility of the kinetic hypothesis 

 in the future of physics itself, and is inclined to pro- 

 pose to substitute for it the theory of energetics. We 

 shall see, in every case, that this other conception, as 

 universal as the kinetic theory, tJie theory of Energy, 

 causes a vivid light to penetrate into the depths of the 

 most difficult problems in physiology. 



Such are, with their successive transformations, the 

 three principal theories, the three great currents 

 between which biology has been tossed to and fro. 

 They are sufficiently indicative of the state of positive 

 science in each age, but one is astonished that they 

 are not more so; and this is due to the fact that these 

 conceptions are too general. They soar too high above 

 reality. More characteristic in this respect will be 

 particular theories of the principal manifestations of 

 living matter, of its perpetuity by generation, of the 

 development by which it acquires its individual form, 

 on heredity. It is here that it is of importance to 

 grasp the progressive march of science — that is to say, 

 the design and the plan of the building which is being 

 erected, " blindly, so to speak," by the efforts of an 

 army of workers, an army becoming more numerous 

 day by day. 



