THE PHYSICAL BASIS OF LIFE 197 



whole structure is arranged on a fundamental plan or style, like, 

 for instance, the ring of carbon atoms in the two substances just 

 mentioned. There is, therefore, a molecular architecture, and, 

 as in ordinary architecture, there are differences of style and 

 of general plan, Gothic, Norman, etc., with endless variety in 

 detail. Amongst the recognised styles of molecular architecture 

 is the proteid style, and the qualities common to all forms of life 

 are based ultimately upon the essential features of that style, 

 while the differences between one kind of living matter and 

 another are the expression of the differences in detail — the 

 omission of this group, the addition of that. 



Some of the atomic groups which find a place in the proteid 

 molecule are readily recognisable by chemical tests — one of 

 these groups occurs as a separate chemical substance called 

 Tryptophane. It shows a vivid purple colour with sulphuric 

 acid and reduced oxalic acid. Here are solutions of two 

 proteids, one from maize seeds, the other from the white of 

 egg, the one of the vegetable strain, the other of the animal 

 strain. The former lacks, the latter possesses this group. 



Now, in order to represent the great varieties of living matter 

 the proteid molecules must be capable of very many variations of 

 structure. That is, after all, mainly a question of size — the larger 

 it is the greater the possibility of variations in detail ; and as the 

 molecule of proteid seems to contain from ten to thirty thousand 

 atoms, whereas the most complex molecule known to the organic 

 chemist contains less than a hundred, there is no lack in this 

 respect. 



Proteids unquestionably are the material basis of life, but 

 when isolated after the death of the cell they are not living. 

 They are chemically stable bodies. They show no signs of the 

 characteristic chemical flux. It is therefore conjectured on 

 experimental grounds that the living molecule is built up of 

 proteid molecules, that it is so complex, so huge, as to include 

 as units of its structure even such large molecules as these. But 

 when such very large molecules enter into chemical combination 

 with one another, whether by reason of the great magnitude of 

 the masses of matter in each in relation to the magnitude of the 

 directive forces, or because the molecules themselves, owing to 

 their great size, to a certain extent cease to be molecules at all in 

 the physical sense, and possess the properties of matter in mass, 

 it is at any rate certain that in their chemical combinations they 



