82 SCIENCE PROGRESS 



manifestations of vital phenomena. This is all pure gain — ^we 

 are beginning to understand more precisely what are, in space 

 and time, in intensity and degree, the physical accotnpaniments 

 of the process we call life. 



Side by side with the development of instrumental methods 

 has gone the development of biochemistry. The precise 

 methods of analysis and synthesis employed by the organic 

 chemist have been applied successfully to the ingoings and the 

 outcomings of the living cell and of the chemical bodies of 

 which it is composed. There are still unknown factors in our 

 food, in the air we breathe, and in the chemical bodies we 

 excrete ; but, on the whole, the study of the imports and exports 

 of the body is well advanced. Our knowledge, however, of the 

 intervening chemical stages of the process, of the intermediate 

 " metabolism " of the cell, or plant, or animal is as yet in its 

 infancy, and the results achieved are more suggestive than 

 conclusive. The essential difficulty of the study is that the pro- 

 cesses of life take place, not in a homogeneous system, not even 

 in a heterogeneous system of a simple kind, but in a tiny complex 

 structure possessing spatial as well as chemical and physical 

 properties — spatial properties which render the ordinary " mass" 

 methods of the chemist incapable of following the finer details 

 of the process. Doubtless great advances are still to come 

 in physiology from such chemical methods, but if we reflect 

 that the living cell is a process and not a thing, and that the 

 sequence of events in a process may well elude the study of the 

 medium in which the process works, we may expect advance to 

 become more rapid with the adoption of micro-chemical or 

 physical methods more capable of coping with the spatial diffi- 

 culties of the problem. One does not know when or where such 

 methods will arise ; there is no doubt, however, that — like the 

 chemical molecule — the living cell and its processes exist in 

 space as well as time, and in a space so small that none of our 

 ordinary means are adequate for its investigation. It would 

 seem likely that the methods by which the spatial structure 

 of the crystal, the molecule, and the atom are being exposed 

 by recent physical investigation will be required before the 

 mechanism of the life processes can be followed in detail. The 

 most fundamental advance, therefore, in biochemistry probably 

 waits on further discoveries in physics. 



A third line on which great developments in physiology j 

 have been made in recent years is in the study of colloid 

 chemistry, and of the physical and electrical properties of 

 solutions. The medium in which occur the processes con- 

 stituting life has certain characteristic physico-chemical pro- 

 perties, and many of the manifestations of life depend upon 

 the colloidal nature of the protoplasm, and of the fluids 



