490 The University Science Bulletin. 



Again it is interesting to note that the changes in the clot are 

 different in the case of these two activities. The migrating cells 

 liberate a substance which occasions a coagulation of the clot. 

 About the contracting fragments from which no cells are growing 

 no such changes are seen in the clot. Contraction in the isolated 

 cells commences after they have ceased to migrate and show these 

 changes. 



The substance or substances liberated by the heart which pre- 

 vents its contraction and which are evidently concerned with this 

 act of contraction are soluble substances. They can be washed 

 away with serum. The evidence gleaned from the above studies 

 on the migrating cells indicates that the substance or substances 

 which occasioned their migration are insoluble in the medium. They 

 are adsorbed or chemically combined with the fibrinogen to form 

 fibrin. The substances which accumulated to stop the activity of 

 the heart is not the "L" substance noted above. 



For the testing of the connective tissue and undifferentiated heart- 

 muscle cells I have used a glass culture chamber (plate LII) instead 

 of the one described in the previous paper.-'' Otherwise the technic 

 was the same. 



During the course of the study of the contracting heart-muscle 

 ■cells in 1912 I had thought that the migrating cells move more rapidly 

 .against the stream and that they became more dispersed in these 

 cultures than in the simple hanging drops of medium. These differ- 

 -ences were observed, however, in but a few cultures. Later I noticed 

 that the thickness of the layers of medium also affected the move- 

 ment of the cells. The cells migrating from 1 mm. thick fragments, 

 which had been placed near the edge of the hanging drop, moved 

 more actively in the thin edge'^ than in the thicker parts of the layer 

 within.^ Regulating these conditions in the "wick cultures," I found 

 that the flowing serum in no way affected the migrating heart- 

 muscle cells, nor did it effect in, any way the movement of the 

 epithelial and connective-tissue cells in general. The only cells 

 :affected were the leucocytes and lymphocytes. In the simple hang- 

 ing-drop cultures it takes several transplants to effect a complete re- 

 moval of the leucocytes and lymphocytes from fragments of bone 

 marrow, lymph gland and spleen. In these "wick cultures" I found 

 fragments of spleen entirely stripped of these cells after seventy-two 

 hours. The leucocytes and lymphocytes had accumulated in masses 

 ■£it tangled parts of the wick. 



The conditions which regulate the movement of these latter cells 



