46 THE CIRCULATING LIQUIDS OF THE BODY 



p. 66), or by perfusing the hind-legs of frogs with a saline solu- 

 tion containing serum. Plasma derived from blood in which the 

 platelets have been prevented from breaking down, and which 

 therefore remains unclotted, has no such effect, or a much slighter 



Fig. 7. Sheep Artery Rings. At 14 and 16 Ringer's solution was replaced by citrate 

 plasma (two different specimens). At 15 and 17 the plasmas were replaced by 

 the corresponding sera. At 18 and 19 the sera replaced Ringer's solution directly. 

 Time-trace, half-minutes. Tracings reduced to J. 



effect. But when the platelets are separated from the plasma 

 and then decomposed, the resulting extracts of platelets are rich 

 in vaso-constrictor material. In the sealing of wounded vessels 

 the platelets would therefore appear to play a double role, yielding 



Fig 8. Frog Perf usion Experiment with Serum. The drops of liquid flowing through 

 the preparation are recorded. At n citrate plasma was injected; at 13 the 

 corresponding citrate serum. The tracing is to be read from left to right. 

 Time is marked in half -minutes 



a substance which causes constriction of the vessel in the neigh- 

 bourhood of the wound while a plug of clot is being formed, thanks 

 to other substances liberated from the platelets, which take an 

 essential part in coagulation. The vaso-constriction may perhaps 



