136 HANDBOOK OF PHYSIOLOGY. 



paraglobuliu, obtained by the saturation method, be added to hydrocele 

 fluid, clotting soon follows, as it will also in a mixed solution of fibrin- 

 ogen and paraglobulin, both obtained by the saturation method. From 

 this it is evident that in plasmine there is something more than the two 

 bodies above mentioned, and that this something is precipitated with 

 the paraglobulin by the saturation method, and is not precipitated by 

 the carbonic acid method. 



The following experiments show that this substance is of the nature 

 of a ferment. If defibrinated blood or serum be kept in a stoppered 

 bottle with its own bulk of alcohol for some weeks, all the proteids are 

 precipitated in a coagulated form ; if the precipitate be then removed 

 by filtration, dried over sulphuric acid, finely powdered, and then sus- 

 pended in water, a watery extract may be obtained by further filtration, 

 containing but little proteid. Yet a little of this watery extract will 

 produce coagulation in fluids, e.g., hydrocele fluid or diluted plasma, 

 which are not spontaneously coagulable, or which coagulate slowly and 

 with difficulty. It will also cause a mixture of fibrinogen and paraglob- 

 ulin both obtained by the carbonic acid method to clot. The watery 

 extract appears to contain the body which is precipitated with the 

 paraglobulin by the saturation method. Its active properties are en- 

 tirely destroyed by boiling. The amount of the extract added does not 

 influence the amount of the clot formed, but only the rapidity of clot- 

 ting, and moreover the active substance contained in the extract evi- 

 dently does not form part of the clot, as it may be obtained from the 

 serum after blood has clotted. So that the substance contained in the 

 aqueous extract of blood appears to belong to that class of bodies which 

 promote the union of, or cause changes in, other bodies, without them- 

 selves entering into union or undergoing change; these are known as 

 ferments. It has, therefore, received the name fibrin ferment or throm- 

 bin. This ferment is developed in the blood soon after it has been 

 shed, and its amount continues to increase for some little time (p. 

 133). 



So far we have seen that plasmine is a body composed of three sub- 

 stances, viz., fibrinogen, paraglobulin, and fibrin ferment. But we shall 

 see that only two of them are necessary to coagulation. 



Relation of Calcium Salts to Coagulation. Blood will not 

 clot except in the presence of soluble calcium salts. If potassium or 

 sodium oxalate be added to blood as it is drawn from the vessels in quan- 

 tities sufficient to precipitate the calcium salts, coagulation will no 

 longer occur. But blood which has thus lost its coagulability may be 

 made to clot upon the addition of soluble calcium salts in proper propor- 

 tion. This fact has been demonstrated not only for blood, but for solu- 

 tions of pure fibrinogen. 



T/ieorics of Coagulation. All present theories of coagulation agree 



