Burrows: Study of Body Cells. 491 



are evidently different from those which control the movements of 

 the fixed tissue cells of the body. Migratory movements and growth 

 of the heart-muscle cells are effected by a substance which is insol- 

 uble in circulating body fluids. Growth in these cells is therefore a 

 purely physico-chemical reaction which proceeds to a condition of 

 static equilibrium. For growth to take place it is necessary that 

 this substance or these substances be removed. As they increase all 

 activity ceases. This substance or substances I have designated 

 as "L." 



DISCUSSION AND CONCLUSIONS. 



From these observations there seemed little doubt, therefore, that 

 the dynamic state of the organism is not in any sense an indication 

 of a similar dynamic state in the cell. It is a product of the organi- 

 zation of the body. In early life the dynamic state is associated 

 with the formation of a substance or substances which combine with 

 or otherwise remove the "L" substance of the cell and occasion an 

 active metabolism within them. This substance has strong affinities 

 for water. It is thus directly concerned with the early building of 

 the organism. It stimulates not only an excessive metabolism in 

 these cells, but also may occasion the primary swelling of the mass. 

 This substance disappears, or rather it ceases to be recognizable, in 

 the early period of development. Subsequent to this period, life be- 

 comes subservient to new organizations. The new organizations, the 

 general nature of which I have illustrated in the study of the rhyth- 

 mical contractions of muscle cells, are not unique, however, for the 

 tissue. They are peculiar to all functioning cells. The nerve fibers 

 are stretched between the brain and an end organ. Adrian has 

 shown that the "all or nothing" law holds for this tissue like it does 

 for the heart. The same is true for the glands. The secretory cells 

 are cells which have a free end and one attached to a basement 

 membrane. Stop up the ducts of one of these glands and these cells 

 undergo atrophy. Such observations are wholly in line with the gen- 

 eral facts which are Imown concerning development. In man the 

 kidney may form tubules up to the tenth day after birth. Other 

 organs cease their progressive growth much earlier. No careful 

 studies are known concerning the time the heart cells cease to divide. 

 In the later embryonic period, at least, all growth in the heart is 

 represented by an increase in the size of the fibers rather than an in- 

 crease in the cells. In the kidneys and glands it manifests itself in 

 a dilation and increase in length of tubules and a flattening of their 



