BLOOD AND LYMPH 247 



precipitated by hydrochloric acid it is more easily soluble in an excess of 

 the reagent. 



When blood coagulates and the usual clot forms, a light yellow fluid 

 exudes. This is blood serum. It differs from blood plasma in contain- 

 ing a large amount of fibrin ferment, a body of great importance in the 

 coagulation of the blood, and also in possessing a lower protein content. 

 The protein material present in plasma and not found in serum is the 

 nbrinogen which is transformed into fibrin in the process of coagulation 

 and removed. The specific gravity of the serum of human blood 

 varies between 1.026 and 1.032. If blood be drawn into a vessel and 

 allowed to remain without stirring or agitation of any sort the major 

 portion of the red corpuscles will sink away from the upper surface, 

 causing this portion of the clot to assume a lighter color due to the 

 predominance of leucocytes. This light-colored portion of the clot is 

 called the "buffy coat." 



Beside the protein constituents already mentioned, other bodies 

 which are found in both the plasma and serum are the following: Sugar 

 (glucose), uric acid (urates), urea, fat, amino-acids, enzymes, lecithin, 

 creatine, carbamic acid, cholesterol and its esters, nucleoprotein, acetone 

 bodies, paralactic acid, gases, ammonia, coloring-matter (lutein or lipo- 

 chrome) and mineral substances. In addition to the substances just 

 named the blood doubtless contains a class of substances called hor- 

 mones of which adrenaline is the only one thus far definitely identified. 

 Some of the pathological constituents of blood are proteases, biliary con- 

 stituents and purine bodies. In many pathological conditions certain 

 normal constituents are present in increased amount. 



Normal human blood contains slightly less than o.i per cent of 

 glucose on the average. Strouse 1 in a very recent series of tests places 

 the average glucose content at 0.084 per cent. That the diet influences 

 the sugar content is shown by the fact that two and one-half to four 

 hours after a meal the sugar content has been found to equal 0.18 per 

 cent. 2 In case of glycosuria the blood sugar may increase (hypergly- 

 cemia) to 0.3-1.0 per cent. For the quantitative determination of 

 blood sugar see page 279. 



The determination of the cholesterol content of the blood is assuming 

 clinical importance. Normal blood contains 140-180 mg. per 100 

 grams of blood, or about 0.15 per cent. This value has been found to 

 be increased (hypercholesterolemia) in gall stones, pregnancy, nephritis, 

 diabetes, and arteriosclerosis and syphilis. (See page 285 for quantitative 

 methods.) 



1 Strouse: Bull. Johns Hop. Hasp., 26, 211, 1915. 

 2 Hirsch: Zeit. physiol. Chem., 93, 355, 1915. 



