134 HANDBOOK OF PHYSIOLOGY. 



from the absence of red corpuscles. If some of the plasma be diluted 

 with twice or three times its bulk of normal saline solution,* coagula- 

 tion is delayed, and the stages of the gradual formation of fibrin in it 

 may be conveniently watched. The viscidity which precedes the com- 

 plete coagulation may be actually seen to be due to the formation of 

 fibrin fibrils first of all at the edge of the fluid containing vessel, and 

 then gradually extending throughout the mass. 



If a further portion of plasma, diluted or not, be whipped with a 

 bundle of twigs, the fibrin may be obtained as a solid, stringy mass, just 

 in the same -yay as from the entire blood, and the resulting fluid no 

 longer retains its power of spontaneous coagulability. 



It is not indeed necessary that the plasma shall have been obtained 

 by the process of cooling above described, as if it had been separated 

 from the corpuscles in any other way, e.g., by allowing blood to flow 

 direct from the vessels of an animal into a vessel containing a third or 

 a fourth of its bulk of a saturated solution of a neutral salt (preferably 

 of magnesium or sodium sulphate) and mixing carefully, will answer 

 the purpose and, just as in the other case the colored corpuscles will 

 subside leaving the clear superstratum of (salted) plasma. In order 

 that salted plasma may coagulate, however, it is necessary to get rid of 

 the salts by dialysis, or to dilute it with several times its bulk of water. 



The second question which must be considered is, from what mate- 

 rials of the plasma is fibrin formed? If pksma be saturated with solid 

 magnesium sulphate or sodium chloride, a white, sticky precipitate called 

 by Denis, by whom it was first obtained, plasmine, is thrown down, 

 after the removal of which, by filtration, the plasma will not spontane- 

 ously coagulate. Plasmine is soluble in dilute neutral saline solutions, 

 and the solution of it speedily coagulates, producing a clot composed of 

 fibrin. Blood plasma therefore contains a substance without which it 

 cannot coagulate, and a solution of which is spontaneously coagulable. 

 This substance is very soluble in dilute saline solutions, and is not, 

 therefore, fibrin, which is insoluble in these fluids. 



But there is distinct evidence that plasmine is a compound body 

 made up of two or more substances, not all of which are requisite to 

 form a clot, and that it is not mere soluble fibrin. There exists in all 

 the serous cavities of the body in health, e.g., the pericardium, the peri- 

 toneum, and the pleura, a certain small amount of transparent fluid, 

 generally of a pale straw color, which in diseased conditions may be 

 greatly increased. It somewhat resembles serum in appearance, but in 

 reality differs from it, being in a measure allied to plasma. This se- 

 rous fluid is not, as a rule, spontaneously coagulable, but may be made 

 to clot on the addition of serum, which is also a fluid which has no 



* Normal saline solution commonly consists of a .6 per cent solution of com- 

 mon salt (sodium chloride) in water. 



