THE PHYSICAL BASIS OF LIFE 195 



as a microscopic fragment of living matter, a single cell, so 

 wonderfully compounded, so cunningly devised, as to enshrine 

 without loss all the diverse qualities and powers which the 

 word "penguin" connotes, down to the trivial detail I have 

 described ! There is little wonder that the naturalists of half 

 a century ago gave the problem up in despair. There is cause 

 for wonder and for congratulation that, impelled by the divine 

 dipsomania for research, knowledge has moved so far as to 

 make a beginning in the assaults. 



Given a fulcrum, anything can be moved. The necessary 

 fulcrum was found when attention was directed not, as in 

 Huxley's time, to the more obvious resemblances between the 

 different kinds of protoplasm, but to the less obvious differences. 

 The microscope for the most part fails us here, in the first place 

 because the discrimination between different kinds of matter by 

 the agency of sight is possible only when there are associated 

 differences in optical properties, and when there is the possi- 

 bility of getting a clear image. Now, living matter is singularly 

 free from definite optical differences, and it has the optical 

 characters of ground glass. Therefore, the ultimate refinements 

 of microscopic vision are for the most part wasted upon it. 

 The dead cell exhibits remarkable structural details, but in the 

 act of death there is of necessity a redistribution of matter 

 which obscures and defaces the finer details of the real living 

 structure, and replaces them by structure which is formed in 

 the process of dying. For the material basis of the difference 

 in the strains of living matter we have to look below the limits 

 of microscopic vision, below the limits even of the living mole- 

 cule, to the chemical molecule of which that living matter is 

 built up. 



The nearest chemical approach to living matter is the 

 proteid, the chemical substance of which all protoplasm is, 

 water excepted, chiefly composed. Now, the fulcrum I spoke 

 of, or, better, the thought which loosed the fetters of imagination, 

 was the appreciation of the significance of the fact that proteids 

 chemically are not all alike, and that the strains of living 

 matter differ from one another in the kinds of proteid of which 

 they are built up — that is to say, in their ultimate chemical 

 constitution. 



All proteids are not the same proteids ; there are proteids 

 of men, others of beasts, others of fishes, and others of birds ! 



