722 



SCIENCE. 



[N. S. Vol. VII. No. 178. 



beginning, adolescence, maturing and old 

 age of races of species in the geological 

 past, advanced by Hyatt and later elab- 

 orated so fully by bim and others. I re- 

 flected back to the nature of development, 

 which such geological recapitulation seems 

 to imitate, as a process in which the cellu- 

 lar parts of the individuals are undergoing 

 a constant process of varying, and I con- 

 ceived of the law of recapitulation as an ex- 

 tension of the principle of varying first seen 

 in the cells of the individual to successive 

 organisms. This principle of ' recapitula- 

 tion,' which was taught by Agassiz, empha- 

 sizes at least the wide applicability of vari- 

 ability in organic processes. 



I have been testing, in all conceivable 

 ways, the application of this theory to the 

 facts of biology for the past fifteen years, but 

 for only a short time have I been aware of 

 the revolutionary nature of the conception. 



As I discover no escape from the essential 

 validity of the proposition, and because of 

 the importance of it for future investiga- 

 tions, and because few biologists with whom 

 I have spoken seem to understand the im- 

 portance of the problem at issue, it may not 

 be inappropriate to attempt at this time to 

 state the foundation upon which the theory 

 appears to rest. 



THE SOUECE OF OUR KNOWLEDGE OF 

 ORGANIC PHENOMENA. 



One of the difficulties standing in the 

 way of forming clear and distinct notions 

 of organic phenomena lies in the fact that 

 we are not accustomed to orient them in 

 their exact relationship to the current no- 

 tions of physical and mathematical science. 



When we contemplate a physical body of 

 matter as growing, varying, inheriting, ac- 

 quiring characters or selecting, the body 

 which performs these acts so far transcends 

 anything which the physicist knows about 

 simple masses of matter, and the perform- 

 ances so far transcend the kind of work he 



is accustomed to deal with, that, as a phy- 

 sicist (whatever his opinion may be of biol- 

 ogists), he frankly confesses he has no 

 knowledge in the case. Without attempt- 

 ing any metaphysical discussion, and with- 

 out stating whether the biologist does or 

 does not know any more than the physicist 

 in the matter, we may join hands with the 

 latter in the belief that if anything is 

 known about them it can be expressed in 

 scientific terms only by an analysis of the 

 observed phenomena in the case. 



In seeking, therefore, for the fundamen- 

 tal characteristic of a living organism we 

 ask, first, how does it differ, phenomenally, 

 from a similar body not organic ? 



If we consider ultimate chemical or 

 physical constitution we discover no funda- 

 mental distinction between a living organ- 

 ism and the same body of dead matter. 



The same chemical elements compose 

 them ; the same physical properties pertain 

 to each. Even mechanically, it is perhaps 

 impossible to define wherein they differ. 



AVhen we observe the functions of the 

 oi'ganism we note certain phenomena in 

 the living body not operating in the same 

 body after death ; but in all these functions 

 we discover none which are not like those 

 of dead bodies of matter in this respect that 

 a specific amount of equivalent of heat- 

 energy is used in their operations, and the 

 energy used is transformed from some other 

 condition, as in inert matter, and no energy 

 seems to be gained or lost in the process. 

 Thus in the two aspects of constitution and 

 action of the bodies it is difficult, and 

 probably it is impossible, scientifically, to 

 describe any constant point of difference in 

 quality between an organism and a body of 

 matter which is not alive. 



There is, however, one point of difference : 

 A living body is constantly changing in its 

 material constitution, while an inert body 

 remains the same. An organism persists 

 in becoming different so long as it lives, 



