THE PHYSICAL BASIS OF LIFE i8i 



tain at least 100,000,000 large molecules. A liver 

 cell contains about 4,000,000,000 molecules ; and 

 Professor McKendrick states that " it is reasonable 

 from existing data to suppose that the germinal 

 vesicle might contain a million of millions of organic 

 molecules." Whatever the size of the cell, how- 

 ever, it has always structural and functional differ- 

 entiation, and the powers of contractibility, assimi- 

 lation, and reproduction. Reproduction is one of 

 the most mysterious of the so-called vital functions. 

 Every cell at some period of its life has the power 

 of reproducing its like by a process of budding 

 or division, and the so-called germ-cells of the multi- 

 cellular organisms have the power when fertilised of 

 initiating a process of growth and division which 

 ends in the production of an individual composed 

 of groups of coherent cells differing in appearance 

 and in function. 



Besides their special powers of assimilation, con- 

 traction, and reproduction, cells have great chemical 

 energy. " In the infinitesimal liver cells," says Carl 

 Snyder, " at least ten or twelve distinct ferments 

 have been found manufacturing various kinds of 

 sugars, and acids, and urea, and bile, and colour- 

 stuffs ; they take up various poisons and render 

 them harmless, bind up the acids with diverse 

 substances to form others more complex, and in 

 the meantime must see that they themselves get 



