Burrows: Study of Body Cells. 497 



activity in early life is dependent upon the synthesis of a substance 

 which combines or otherwise removes the "L" substance. In later 

 life it is dependent upon a mechanical differentiation. This form 

 of synthesis in later embryonic life forms a substance which is 

 fibrinogen or closely akin it. This forms an insoluble compound 

 with "L" rather than the soaplike substance of the earlier period. 

 In the proper environment it occasions, through its coagulation, the 

 form necessary for the dynamic state. 



By these observations it has been possible, therefore, for the first 

 time to define differentiation in other than morphological terms, 

 and to compare function with growth. The growth of the undiffer- 

 entiated cells of early life is the result of a special synthesis. The 

 development of function is the result of a slightly different one. 

 Differentiation is quite different, therefore, from what it has been 

 conceived to be. 



While these observations reduce growth and function to simple 

 physicochemical formulation, they give no hint as to the cause for 

 this change in synthesis from early to late life. Any substance 

 which removes the "L" causes an immediate loss of mechanical 

 differentiation. The heart-muscle cells in contact with the fibrin 

 become simple mesenchyme cells. Only under proper mechanical 

 conditions can they redifferentiate. What is true for the heart is 

 true for the glands. In the cultures the gland cells stretch to form 

 membrane like the skin. They lose the form necessary for function. 



These facts, again, do not explain chemical differentiation. In 

 the above observation I have also not discussed all the deficiency of 

 these cells. Besides the lack of any organization for work and any 

 means within themselves to allow the energy-producing reaction to 

 proceed under the ordinary conditions in nature, they are also bereft 

 of the property of using the crude material of nature for this energy- 

 producing reaction. While energy production in the body is derived 

 chiefly from H and C, these cells cannot use the sugar carried to 

 them by the blood stream without intervention of substances from 

 the pancreas. The organization of the whole or certain of its parts 

 are again essential for another of their important needs. 



It is upon this last deficiency that the chemical syntheses peculiar 

 to differentiation must depend. The body is a machine operated like 

 any other machine in nature. Its metabolism has no complexities, 

 as most biologists would have it. It is a machine which is able to 

 produce energy and transform it into work. It has been possible to 

 locate these different reactions. The energy is produced in the cell; 



