Burrows: Study of Body Cells. 495 



ganglion cells. In men I think it is very questionable whether the 

 nervous system, any more than the striated muscle or gland cells, 

 respond without the aid of external conditions. It is upon this fact 

 that coordination depends. 



There is no evidence from the above observations that the cells 

 themselves undergo any absolute changes during these fundamental 

 changes in the body. For a good many years it has been well 

 known that bone and cartilage are products of a given organiza- 

 tion of the part and not a product of the cell. It has been shown, 

 for instance, that bone will develop in the pelvis of the kidney if 

 the blood vessels to that organ are ligated. Asami and W. DocTi^^ 

 repeated these experiments in the laboratory and proved completely 

 the existence of these changes, as the other authors had shown. In 

 the tissue culture the cells migrate readily, not only from fragments 

 of interstitial tissue, tendons and fascia, but also from fragments 

 of bone and cartilage. The bone cells and cartilage cells behave in 

 every way like the other connective-tissue cells. The bone and 

 cartilage remains behind like the extracellular fibrils. In the same 

 way the adult muscle fiber will not react in the plasma, but I have 

 seen the nucleus and sarcoplasm migrate out and leave the adult 

 fiber behind. In the plasma this mass forms perfect connective- 

 tissue cells. These cells react also in every way like the ordinary 

 connective-tissue cells. 



Such simple fluid systems may not only suffer changes in shape 

 and differential changes of tension at various points on their sur- 

 face, but thej^ may also suffer additions and probably subtractions 

 from themselves. In the body differentiation is not only the result 

 of mechanical changes initiated and controlled by the environment, 

 but it may be also chemical in nature. As the above studies of the 

 skin epithelium show, these cells do not suffer fundamentally from 

 the connective-tissue cells. For metabolism to take place within 

 them it is necessary that the ''L" substance be removed from them. 

 This "L" substance is not different in these cells from that of the 

 connective-tissue cells. These cells differ from the connective tissue 

 in that they also contain a proteolytic ferment. The pancreas cells 

 again differ in that they also contain a fat-splitting ferment. They 

 often fail to migrate into the clot. They lead rather to the rapid 

 splitting of the fat of the plasma to fatty acid crystals. This pre- 

 vents also the migration of the connective-tissue cells from these 

 fragments into the medium. So in each case the various tissues 

 differ as they contain their own peculiar added products. The fun- 



