488 The University Science Bulletin. 



the fibrinogen. This substance formed early in the life of the cul- 

 ture. It spreads rapidly to cover the whole of the medium. The 

 cells later invade it as they invade the plasma. It differs from the 

 fibrinogen in that it is a much more active stimulant. The cells 

 form no insoluble compound with it. They grow actively for a time 

 within it and invariably disintegrate. In the plasma cultures of 

 these younger cells, a part of the cells may at first invade the clot. 

 They soon leave the fibrinogen, however, for the surface film which 

 has stronger affinities for them. Single cells may also liberate this 

 substance. 



While I do not know the exact nature of this substance, it is 

 interesting to note here that this substance disappears from or its 

 action is inhibited about fragments of undifferentiated mesenchyme 

 and the heart-muscle tissue in the cultures between the ninth and 

 fourteenth day of the incubator life of the chick embryo. This is 

 not true, however, of other tissue. I have identified it in the epider- 

 mis and the liver of these embryos as late as the eighteenth day. 

 Felix has shown the new tubules developed in the kidney of man as 

 late as ten days after birth. While these studies are yet incom- 

 plete, they do indicate that the disappearance or the inhibition of 

 the action of this substance is not regular, but takes place at irregu- 

 lar times in different tissue of these higher animals, and that this 

 disappearance corresponds to the forms taken by the developing 

 embryo and adult. 



What might be the exact chemistry of this substance remains to 

 be seen. It seems most plausible, however, that the secrets of the 

 building of the body will be found in the physical properties of it. 

 These physical properties are, first, a strong affinity for water, 

 and, second, an ability to stimulate an excessive metabolism. 



From the above observation it became evident, therefore, that the 

 cells of the body are not in a continuous state of activity. The 

 activity of early life is dependent completely upon the synthesis of 

 a substance which removes the "L" substance froiH the cells. This 

 substance is gradually superseded in later life by fibrinogen. Fibrin- 

 ogen combines with "L" to form fibrin, an insoluble compound. In 

 the later periods life centers about the functioning or differentiated 

 systems. To prove this fact more definitely it became of interest to 

 study the effect of a flowing stream of serum upon rhythmically con- 

 tracting cells and the dedifferentiated muscle cells and the cells of 

 connective tissue. 



