240 RESEARCH SEMINAR. 



4. Selachians have an osmotic pressure equal to that of the 

 sea water and change with the external medium, although not so 

 readily or completely as invertebrates. They die if the change 

 in osmotic pressure is great. 



5. Marine teleosts have an osmotic pressure only about half 

 that of the sea water ; J = 0.80 and 0.96. Transferring 

 common eels from salt into fresh water did not lower the osmotic 

 pressure of their blood. Fnndulus Heteroclitus could also be 

 placed in fresh water or doubly concentrated sea water and live 

 for weeks. If, however, the body was partly scaled, or part of 

 the skin removed, the fish die in normal sea water and in fresh 

 water, but can be kept indefinitely in sea water which has been 

 diluted with an equal volume of distilled water and which there- 

 fore has an osmotic pressure approximating that of their blood. 

 These experiments point to the normal impermeability of the 

 teleost integument. 



August 12. Coagulation of the Blood. By LEO LOEB. 



In former investigations I made it very probable that the so- 

 called first coagulation of the blood of certain arthropods and 

 the coagulation of the blood of Liinnlits consists in an agglutina- 

 tion of blood cells, that in the second coagulation of arthropods, 

 on the other hand, fibrin is formed from fibrinogen under the influ- 

 ence of substances present in the blood cells and in the tissues. 

 The latter, which I called tissue coagulins, are, within certain 

 limits, specific, the former being not at all or much less specific. 

 Similar conditions are present in vertebrate blood. 



We have therefore to distinguish between two kinds of sub- 

 stances which may, under ordinary circumstances, affect the 

 coagulation of the blood, namely, substances present in the 

 serum and those present in the tissues (tissue coagulins). 



Quite recently several investigators (Morawitz, Fuld u. Spiro) 

 have advanced the theory that the tissue coagulins act only in- 

 directly by transforming (to use the terms of Morawitz) throm- 

 bogen into prothrombin, which, by the aid of calcium, becomes 

 the active ferment. This is a somewhat modified form of 

 Alexander Schmidt's theory of the coagulation of the blood. 

 Certain facts, however, made it appear to me more probable that 



