216 MANUAL OF PHYSIOLOGY. 



firmly adheres to the stirring rods and at once contracts around 

 them. 



CHEMICAL COMPOSITION OF PLASMA. 



On account of the rapid spontaneous formation of fibrin and 

 serum when the plasma is removed from the body and allowed to 

 die, the exact chemical condition of the liquor sanguinis during 

 life cannot be investigated, the separation occurring before the 

 simplest chemical method can be carried out. 



We have no reason to suppose that fibrin exists normally in 

 the blood, but it would appear that this substance is only formed 

 at the moment of coagulation, and is one of the most obvious of 

 many changes which take place at the time of the death of blood 

 plasma. 



The chemical change comprehended under the term coagula- 

 tion occurring when plasma is deprived of its means of vitality, 

 and ending in the production of fibrin and serum, is naturally 

 of the first importance in studying the chemical relationships of 

 living plasma. It can best be followed out in the coagulation of 

 plasma when separated from the corpuscles, for (although the 

 stages in the coagulation of blood are the same, the appearance 

 of an insoluble albumin fibrin being the one essential in either 

 case) the corpuscles complicate the process and modify the ap- 

 pearance of the clot. 



Not only is the fibrin not present as such in the living plasma, 

 but it requires for its production the presence of other substances 

 which either do not exist in the living plasma, or are there so 

 chemically associated as not to bring about the change which 

 occurs when the plasma is dead. 



The reasons for believing this are the following. Fluids- which 

 sometimes collect by a slow process in the serous cavities of the 

 body, e.g., hydrocele fluid, pleural effusion, etc., if kept quite 

 clean do not generally undergo spontaneous coagulation. If to 

 one of these some serum from around a blood clot be added, 

 coagulation takes place just as in plasma (Buchanan). That is 

 to say, we have here two fluids, neither of which coagulates when 

 left to itself, but which do coagulate when mixed together. From 



