THEORIES OF CLOTTING 



307 



under an oil-inmicrsion microscope arc capable of producing 

 intravascular clotting when injected into the blood-stream, while 

 powdered glass or quartz particles of apparently the same size 

 are without effect. Coarser glass suspensions arc necessary to 

 produce the effect. Some other factor in addition to surface must 

 come into play or kephalin particles must have a wrinkled surface. 

 (2) H-ion concentration. This view of the process of blood- 

 clotting has been challenged by Pickering and Hewitt and by others 

 as an incomplete picture. It does not accoiuit for the fact that, if 

 due precautions are taken, l)irds' l)lood, which contains all the 

 constituents necessary for the formation of a clot, remains liquid 

 for a considerable time after removal from the vessels. The 

 addition of a mere trace of acid causes immediate and extensive 

 clotting. From this one may infer that in avian blood the forma- 

 tion of a clot depends primarily on the attainment of a definite 

 hydrogen ion concentration. That this inference is justifiable, 

 not only for birds' blood, but also for mammalian blood, is indicated 

 by experiments where blood was prevented from coagulating by 

 the liberation of alkali in it. Tri-calcium phosphate, the salt of a 

 weak acid, H3PO4, and of a strong base, Ca(0H)2, dissociates in 

 aqueous solution as shown on p. 68, liberating -OH ions, and so 

 tending to reduce the hydrogen ion concentration of the solution. 

 Thus : 



Ca3 (POJ^ 



+ 2P0, 



6H2O 



^ 3Ca (OH), + 2H3PO4 



(strong base) (weak acid) 



Now, when tri-calcium phosphate is added to mammalian blood, 

 some of the salt dissociates, liberating alkali, and so preventing 

 clotting. Further, it has been found that fibrinogen in the 

 presence of the serum proteins, with their non-diffusible calcium, 

 readily forms an insoluble complex gel with a phosphatide in a 

 slightlij acid medium. Confirmation of the part played in this 

 process by the ^^H of the blood is deducible from Kugelmass' 

 investigations on the change in /jH of the blood during coagulation. 

 Blood has a pH of 7-4, but the optimal pH for the process of clot- 

 ting is 7. From such experiments, the conclusion may be drawn 

 that alkali is the factor in the blood which prevents intra-vascular 

 clotting. As we shall see later, blood has a considerable alkali 

 reserve (buffering power), so that a tendency to reduce the 

 hydrogen ion concentration is restricted within narrow limits. 



(3) Calcium. During coagulation the electrical conductivity of 



20—2 



