252 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



exposed, with a wealth of detail that set the subject in a new light, 

 the far-reaching influences of physical forces on the growth and ulti- 

 mate confonnation of organisms and the parts of organisms. 



While the structures, the "things seen" in the architecture of ani- 

 mate nature, have been yielding their secrets to such physical analy- 

 sis, the activities of living stuff, far less easy to comprehend, and yet 

 more intimately part of life than the material plasms through which 

 they are expressed, have also been giving way to the skilled attacks 

 of the physicist and chemist. Here investigation has naturally been 

 concentrated upon the unit of organization, the cell, and it has shown 

 that just as the cell boundary is determined by physical forces, of 

 surface tension, so activities of the living cell membranes, which 

 form its boundary, also fall into line, so far as analysis goes, with 

 physicochemical laws. Thus the living cell, of plant or animal, acts 

 as an osmotic system, as de Vries showed long ago with the leaf cells 

 of Tradescantia and as has been shown for many animal cells such as 

 mammalian red blood cells and leucocytes, spermatozoa, muscle cells 

 of frogs, and egg cells of echinoderms. Moreover, the adjustment 

 of forces within and without living cells has been found to be in ac- 

 cordance with the thermodynamical balance known as the "Donnan 

 equilibrium" or "membrane equilibrium," which interprets the rela- 

 tionship between solvents separated by a membrane, on one side of 

 which is a nondiffusible ion or molecule. (For a summary of the 

 biological aspect, see Dixit, 1938.) Part of the activity of a cell, 

 at any rate, is amenable to purely physicochemical explanation. 



Further understanding of the activities of the cell as well as prac- 

 tical benefits to humanity have followed upon the enzyme discoveries 

 of recent years. I would remind you of only one example, that the 

 digestive enzyme of the papaya plant, papain, is now used in Amer- 

 ica by the ton in making tough meat tender. As Balls (1938) put it, 

 in an address to the Washington Academy of Science, " we should 

 probably all be surprised to know the exact number of years of 

 beef life that is taken out of the steaks of America by means of 

 papain"; though I have a strong suspicion that knowledge of this 

 great discovery has not yet penetrated to the roast beef of old Eng- 

 land. As regards cell activity the enzymes act as catalysts speed- 

 ing up chemical reactions; without enzymes cell processes would 

 "proceed so slowly that the cell would die waiting for food to be 

 digested or oxygen to become available" (Balls, 1938). 



From these few examples it is patent that much that was myste- 

 rious about life has disappeared or is disappearing before the per- 

 sistent inquiries of the physicist and chemist. Life processes of the 

 physiological order are ruled and guided by the selfsame laws which 

 regulate action in the nonliving world. 



