294 THE BLOOD. 



function of the leukocytes and the elaborate arrangements for 

 their production in the body ; (2) their congregation and great 

 reproduction in the intestinal area during a proteid meal ; (3) the 

 positive chemotaxis they exhibit toward the proteids, albumoses, 

 and other products of digestion ; (4) the maintenance of the pro- 

 teid constituents of the blood during fasting ; (5) the fate of the 

 bodies of the leukocytes when they disintegrate ; (6) the fact that 

 no products of digested proteids are found in the blood during 

 proteid digestion. It would make the leukocyte, in fact, a store- 

 house of the surplus proteid food of the body, just as the liver- 

 cell is a storehouse of surplus carbohydrate food." 



Nucleoproteid. In regard to this constituent of plasma, Schiifer 

 says that it is doubtful if it exists in the plasma of circulating 

 blood, and that beyond the fact of its appearing to be one of the 

 essential factors in the formation of fibrin, very little is known 

 about it. It is regarded as being derived from the leukocytes and 

 plaques at the time the blood is withdrawn from the vessels. A 

 small amount comes from the red corpuscles. The reasons for 

 this belief as given by Schiifer are : 



1. White blood-corpuscles and similar cells (lymph-cells, thy- 

 mus-cells, etc.) always contain a considerable amount of nucleo- 

 proteid. 



2. In plasma obtained by subsidence of the corpuscles there is 

 most nucleoproteid in the lower layers, which contain most leuko- 

 cytes ; and least in the upper, which contain very few. 



3. Fluids which collect in the serous cavities of the body 

 (pericardial fluid, hydrocele fluid, ascitic fluid) frequently contain 

 no leukocytes. When this is the case they are also devoid of 

 nucleoproteid and of the property of spontaneous coagulability, 

 although they contain fibrinogen. Solutions of this nucleoproteid 

 are coagulated at 65 C., and at 60C., if free alkali is present, it 

 is split into nuclein and a proteid. If soluble salts of lime are 

 present, the nucleoproteid unites with the lime, and the product 

 has the property of converting fibrinogen into fibrin, and is 

 identical with fibrin-ferment or thrombin; inasmuch as the nucleo- 

 proteid precedes and becomes changed into thrombin, it is termed 

 prothrombin. 



Gases. The plasma contains oxygen and nitrogen in solution, 

 and carbon anhydrid both in solution and also in combination as 

 sodium carbonate and bicarbonate. The amount of oxygen in 

 the plasma is very small : in the dog, 0.25 per cent. 



Coagulation of Blood. When blood is withdrawn from 

 the circulation it undergoes coagulation, consisting in the produc- 

 tion of a clot from which is subsequently expressed a fluid the 

 serum. The length of time required for coagulation varies in the 

 blood of different animals. In human blood the change manifests 

 itself in about two or three minutes. When the blood is withdrawn 



