438 BIOLOGY IN EELATION TO OTHER NATURAL SCIENCES. 



altliough peiliaps it does uot express it, that action is not an attribute 

 to the organism but of its essence — that if, on the other hand, proto- 

 plasm is the basis of life, life is the basis of protoplasm. Their rela- 

 tions to each other are reciprocal. We think of the visible structure 

 only in connection with the invisible process. The definition is also of 

 value as indicating at once the two lines of inquiry into which the sei- 

 ence has divided by the natural evolution of knowledge. These two 

 lines may be easily educed from the general principle from whicli Tre- 

 viranus started, according to which it is the fundamental characteristic 

 of the organism that all that goes on in it is to the advantage of the 

 whole. 1 need scarcely say that this fundamental conception of organ- 

 ism has at all times presented itself to the minds of those who have 

 sought to understand the distinction between living and non-living. 

 Without going back to the true father and founder of biology, Aris- 

 totle, we may recall with interest the language employed in relation to 

 it by the physiologists of three hundred years ago. It was at that time 

 expressed by the term consensus imriium — which was defined as the 

 concurrence of parts in action, of such a nature that each does quod 

 suum, est, all combining to bring about one eftect "as if they had been 

 in secret council," but at the same time constanti quadam naturce lege.* 

 Prof. Huxley has made familiar to us how a century later J)escartes 

 imagined to himself a mechanism to carry out this consensus, based on 

 such scanty knowledge as was then available of the structure of the 

 nervous system. The discoveries of the early part of the present cen- 

 tury relating to the reflex action and the functions of sensory and 

 motor nerves, served to realize in a wonderful way his anticipations as 

 to the channels of influence, afferent and eflerent, by whicli the consen- 

 sus is maintained; and in recent times (as Ave hope to learn from Prof. 

 Horsley's lecture on the physiology of the nervous system) these 

 channels have been investigated with extraoidinary minuteness and 

 success. 



Whether with the old writers we si)eak about consensus, with Trevi- 

 ranus about adaptation, or are content to take organism as our point of 

 departure, it means that, regarding a plant or an animal as an organ- 

 ism, we concern ourselves primarily with its activities, or, to use the 

 word which best expresses it, its energies. Now the first thing that 

 strikes us in beginning to think about the activities of an organism is 

 that they are naturally distinguishable into two kinds, according as we 

 consider the action of the whole organism in its relation to the external 

 world or to other organisms, or the action of the parts or organs in 

 their relation to each other. The distinction to which we are thus led 

 between the internal and external relations of plants and animals has 

 of course always existed, but has only lately come into such prominence 

 that it divides biologists more or less comjjletely into two camps — on 



*Bausner, De Consensu Partium Eumani Corporis, Amst., 1556, Prief. ad lectorem, 

 p. 4. 



