1913] Holmes: Ectodermic Epithelium of Tadpoles 159 



in the coagulated plasma, partly perhaps because their spreading 

 is less impeded, but also, I suspect, because the tissues thrive 

 better in plasma and therefore have an antagonistic influence on 

 the development of these organisms. It was often noticed that, 

 while bacteria may be present in preparations of thriving cells, 

 they often did not make much headway as long as the tissues 

 were active. 



As a rule the young embryos or tadpoles were cut into small 

 pieces in sterile Ringer's solution. Both blood plasma and lymph 

 were used as culture media. The latter is much more convenient 

 to work with, as a drop of lymph can be easily transferred without 

 coagulation by a sterile paraffin-coated pipette from a lymph 

 sac of the adult to a cover slip. The piece of tissue was then 

 placed in a drop of lymph and the cover slip sealed by pure 

 vaseline over the cavity of a hollow ground slide. The lymph was 

 often centrifnged to free it from corpuscles, but for the purpose 

 of many experiments this operation was not necessary. No notice- 

 able advantage resulted from using plasma diluted with distilled 

 water, which was found by Carrel to be so valuable a medium 

 for mammalian tissue. Both Ringer's and Locke's solutions were 

 used as culture media, but while cells remained alive and active 

 in these fluids for several days, and even weeks, they were not 

 found nearly so suitable as lymph and plasma, or even serum. 

 As a rule each culture was made in blood plasma or lymph 

 of its own species. Cells of the tadpoles of Hyla, Rana, and 

 Diemyctylus would live and manifest some activity in the lymph 

 or plasma of other amphibians, but they did not thrive so well 

 as in fluids from members of the species to which they themselves 

 belonged. The tissues in the earlier experiments were kept at 

 ordinary room temperature, but later they were placed in an 

 ice chest whose temperature varied from 8° to 15° C. where they 

 thrived better and lived longer. Many preparations remained 

 alive at ordinary temperature for over two months. At intervals 

 of from a few days to a week the tissues were usually transferred 

 to fresh lymph or plasma. Several preparations, however, were 

 kept alive for over six weeks without change of medium. When 

 the changes were made the pieces of tissue were washed for 

 several minutes in Ringer's solution before being placed in fresh 



