30 THE FUNCTIONS OF ANIMALS. 



protoplasm. This is a mere truism. We do not know the 

 nature of this living matter ; perhaps our most certain know- 

 ledge of it is, that in our brains its activity is associated with 

 consciousness. 



When more is known in regard to the chemistry and 

 physics of living matter, it may be possible to bring vital 

 phenomena more into line with the changes which are 

 observed in inorganic things. At present, however, it is 

 idle to deny that" vital phenomena are things apart. Not 

 even the simplest of them can be explained in terms of 

 chemistry and physics. Even the passage of digested food 

 from the gut to the blood vessels is more than ordinary 

 physical osmosis ; it is modified by the fact that the cells 

 are living. 



But though we cannot analyse living matter, nor thoroughly 

 explain the changes by which the material of the body 

 breaks down or is built up, we can trace, by chemical 

 analysis, how food passes through various transformations 

 till it becomes a usable part of the living body, and we can 

 also catch some of the waste products formed when muscles 

 or other parts are active. 



In this way we learn that waste products are invariably 

 formed when work is done, and that living animals have 

 a marvellous power of rapid repair, of ceaselessly changing, 

 and yet remaining more or less the same. Theory begins 

 when we attempt to make the general idea of waste and 

 repair more precise. In the study of " protoplasm," both 

 morphologist and physiologist have reached their strict 

 limits. Further analysis becomes physical and chemical, 

 and ends in the confession that protoplasm is a marvellous 

 form of matter in motion, or a subtle kind of motion of 

 which we can form only a very vague conception. 



What is known in regard to the structure of protoplasm does not 

 help the physiologist very much. As we shall afterwards see, the 

 microscopists discover an intricate network which pervades each unit 

 of living matter, but no physiologist dreams of explaining the life of a 

 cell in terms of its microscopically visible structure. Yet, as Burdon 

 Sanderson says, "we still hold to the fundamental principle that living 

 matter acts by virtue of its structure, provided the term structure be 

 used in a sense which carries it beyond the limits of anatomical in- 

 vestigation, i.e. beyond the knowledge which can be attained either by 

 the scalpel or the microscope." But, in the end, this means that living 



