118 THE ACTION OF THE LIVING CELL 



After incubation, if the culture medium is suitable, 

 the cells are found to migrate from the periphery of 

 the tissue fragment or explant. This migration takes 

 place only along solid supporting substances; hence 

 blood plasma is usually added to the medium, since 

 after coagulation of the drop, the fibrin threads form 

 a suitable pathway for movement of the cells. 



That the plasma per se is not essential to the cellular 

 migration but simply offers a convenient mechanical 

 support is shovv^n by the fact that glass wool or spider's 

 web immersed in a fluid medium offers a substitute 

 satisfactory for this purpose. (Harrison, 1914.) 



This migration of cells from tissue explants will 

 take place in simple inorganic media such as Locke's 

 solution,^ although in such instances, because of the 

 absence of suitable organic foodstuffs, the cells do not 

 undergo appreciable proliferation and growth. Such 

 experiments, however, demonstrate that the cells of 

 recently killed animals are alive, and are capable of 

 remaining alive in Locke's solution for some time. 

 The duration of life under such conditions varies with 

 the type of tissue and the temperature. For example, 

 at 37° C. kidney epithelium and smooth muscle may 

 live for ten days or longer, while nerve, and skeletal 

 muscle may be kept alive but a few hours. (Lewis, 

 W. H., and Lewis, M. R., 1924.) 



Although migration of cells such as is referred to 

 above increases the area of the explant, no growth as 

 measured by an increased mass of living tissue takes 

 place unless suitable foodstuffs are added to the saline 

 medium. When, however, the composition of the cul- 



'^ Locke's solution contains 0.9% sodium chloride, 0.025% calcium 

 chloride, 0.42% potassium chloride, and 0.02% sodium bicarbonate. 



