492 The University Science Bulletin. 



lining cells. In the wound the exudate is the active stimulus for 

 growth. It stimulates metabolism through a direct affinity of the 

 "L" substance for the fibrinogen. "L" combines with fibrinogen to 

 form fibrin. The fibrin then becomes the extracellular or collagen 

 fibrils. The cells remain active and move towards the center of the 

 exudate until the reaction is satisfied. The end of activity is the 

 completion of the reaction. It is the scar for the connective tissue 

 and continuity, and the limiting membrane for the epithelial cells. 

 Through the analysis of the simple act of changes of shape and 

 the movement of the connective-tissue cells it has been possible to 

 show that these acts are not the result of any complex cellular or- 

 ganization, but a simple reaction between substances in the environ- 

 ment and a substance of the cell. The movement is the result of the 

 cohesion of this substance for the cell on one side and specific sub- 

 stances in the medium on the other. In this act of locomotion the 

 cell supplies the energy; the mechanism otherwise resides wholly in 

 the environment. Again, in other studies I have been able to show 

 that the syntheses for growth are not a part of these energy-pro- 

 ducing reactions, but they are separate reactions. The connective- 

 tissue cells in the adult organism are widely separated in a mass of 

 fibrillar substance. These cells migrate into the plasma, but they 

 do not grow. In the plasma culture, growth is peculiar alone to the 

 more cellular fragments of embryonic tissue, granulation tissue or 

 sarcomata. By, the use of embryonic extracts it is possible to stim- 

 ulate the metabolism of these connective-tissue cells. Under these 

 conditions the widely separated cells of the adult fragments will 

 grow and divide. About the more densely cellular fragments such 

 stimulation is not necessary. It is harmful. It leads to the destruc- 

 tion of the cell, a breaking down of the proteins of the protoplasm. 

 If these same fragments are teased apart so the cells become more 

 dispersed, growth ceases again. For growth to take place it is neces- 

 sary that the cells be either crowded or excessively stimulated. The 

 important factor for this reaction is evidently the concentration of 

 certain products of their metabolism. The concentrating of such 

 products may be induced by the crowding of cells or increasing the 

 rate of their production. These cells liberate not only the "L" sub- 

 stance, but also CO2 and H2O. How many other substances are 

 formed when the reaction is proceeding has not been determined. 

 Protein synthesis is not a part of the ordinary metabolic reaction of 

 the cell. It is secondary reaction depending upon and obtaining the 



