BLOOD-DISKS. 19 



blood undergo disintegration : it is believed that they 

 take an important part in the process, and even contribute 

 the material out of which fibrin is formed. They appear 

 also to be the source of the ferment above mentioned, for 

 plasma filtered at a few degrees above o C. loses its power 

 of coagulating at ordinary temperatures : this power is 

 restored to it by the addition of a ferment, but the quan- 

 tity of fibrin obtained is less than that yielded by unfil- 

 tered plasma. 



The Plasma of blood contains about 0-5 per cent, of the 

 total blood-weight of soluble salts, of which between 0*3 

 and O'4 is sodic chloride, and about O'l sodic phosphate, 

 the remainder consisting chiefly of sodic carbonates. The 

 insoluble calcic and magnesic phosphates, of which plasma 

 contains about 0*04 per cent, of the blood-weight, are held 

 in solution by combination with albumin. Serum also 

 contains a trace of sulphates. 



Serum, i.e., plasma which has been deprived of its 

 plasmin by coagulation, differs from plasma in the absence 

 of fibrinogen. It contains serum-albumin, paraglobulin, 

 and probably alkali-albuminate, besides salts and extrac- 

 tive. The whole of the proteid of serum (albumin and 

 globulin), with the exception of a trace of albuminate, is 

 separated by heat at about 73 C. It is also precipitated 

 by alcohol and by strong mineral acids. 



Plasma contains oxygen and nitrogen in about the pro- 

 portion in which these gases are severally found in water. 

 It contains somewhat more free CO than the serum would 

 absorb if it were so much water. 



! Blood-disks. The coloured blood-corpuscles consist of 

 stroma and haemoglobin. They constitute about a third 

 of the weight of the blood, and contain about 43 per 

 cent, of solids, and 39 per cent, of haemoglobin. The 

 stroma is made up for the most part of substances soluble 

 in ether, viz., lecithin and cholesterin, and of globulins 

 resembling those of plasma. The blood-corpuscles also 



C 2 



