Cell and Protoplasm. 115 



to us in its intrinsic nature) of the living 1 substance, and 

 are active in its smallest particles, since living" matter 

 is neither permanent nor quiescent, but is in more or 

 less constant internal motion." 



"To assimilate and dissimilate is a fundamental pro- 

 perty of living matter, engrained deeply in its nature, 

 and these functions continue, provided the essential 

 conditions of life are present without assistance of 

 external stimuli " ; though such stimuli may compel the 

 living matter to greater activity in either direction. 



Similarly, Prof. Gaskell was led from his study of 

 nervous function to the idea that life implies an alter- 

 nation of two processes one of them a running down 

 or disruption (katabolism), the other a winding up or 

 construction (anabolism). There are minor differences 

 between the two views, but Gaskell's anabolism and 

 katabolism correspond respectively to Hering's assimi- 

 lation and dissimilation. 



Before we leave the subject, it may be well to recall 

 the uncertainties. We have no knowledge of the real 

 nature of living- matter; we cannot define any substance 

 physically or chemically, and say, this is pure protoplasm. 

 According to one view, protoplasm is a mixture of com- 

 plex substances ; according to another view it is a single 

 substance allied to proteids; according to a third 

 perhaps most probable view there is no such thing as 

 living matter. The meaning of the last view, which 

 may appear paradoxical, is simply that vital function 

 may depend upon the interactions or inter-relations of 

 a number of complex substances, none of which could 

 by itself be called alive. Just as the secret of a firm's 

 success may depend upon a particularly fortunate asso- 

 ciation of partners, so it may be with vitality. 



"We are compelled", said Prof. E. B. Wilson in 

 1896, "by the most stringent evidence to admit that 

 the ultimate basis of living matter is not a single chemi- 

 cal substance, but a mixture of many substances that 

 are self-propagating without loss of their specific char- 

 acter." 



Even at an early date biologists recognized that the 

 behaviour of cells, especially in development, necessi- 



