84 A TEXTBOOK OF PHYSIOLOGY 



salt is removed by dialysis, or by great dilution with water. It 

 coagulates at 69 C. to 75 C., and has a levorotatory power of - 47-8. 

 It is possible that it is not one single body, since by differences in 

 solubility and precipitability two bodies have been obtained euglob- 

 ulin, easily precipitated by 28 to 36 per cent, of ammonium sulphate; 

 and pseudo-globulin, requiring 36 to 44 volumes per cent, of this salt. 

 According to some observers, after coagulation has taken place 

 there is found in the serum a fibrin globulin which is formed as a pro- 

 duct when fibrinogen is converted into fibrin. It is apparently almost 

 identical with fibrinogen. 



Fibrinogen is a body of the globulin type, coagulated by heat 

 at about 56 C. It is precipitated from solution by half-satura- 

 tion with sodium chloride. The precipitate may be redissolved in 

 dilute saline, and the solution thus obtained clotted at 37 C. by the 

 addition of a trace of blood -serum. This experiment is important to 

 the theory of the clotting of blood. 



Serum albumin is a body soluble in water and not precipitated from 

 solution by magnesium sulphate. Its coagulation temperature varies 

 according to the amount of salt present in the solution. Dissolved 

 in distilled water it coagulated at about 50 C. ; with salts present in 

 the solution the temperature of coagulation is higher. When a solu- 

 tion of serum albumin almost saturated with ammonium sulphate is 

 allowed to concentrate by standing, crystals of a compound of albumin 

 with the salt fall out. 



The source of the proteins yielded by plasma is not known. The 

 yield of fibrinogen is said to depend on the liver. Blood, the circu- 

 lation of which is confined to the heart and lungs, loses its property 

 of coagulability, whereas blood circulated through the liver has an 

 increased coagulative power. According to one theory of protein 

 metabolism (q.v.), the blood-proteins are formed out of the protein 

 products of digestion at the time of the passage of these through the 

 intestinal wall into the blood. 



The amount of protein yielded by the plasma is said to vary in 

 certain diseased conditions. In cases of infection, such as pneumonia, 

 it is increased, particularly the fibrinogen moiety. Globulins are said 

 to be increased relatively to the albumin (the so-called " protein 

 quotient ") in parenchymatous nephritis. The normal proportion is 

 4 : 3 in man. It varies in different animals. The plasma of cold- 

 blooded animals chiefly yields globulins. In the regeneration of the 

 plasma after haemorrhage the albumin is formed first, and afterwards 

 the globulin. Closely allied to the globulin portion of the blood are 

 the protective substances, such as antitoxins, haemolysiiis, bacterio- 

 lysins, precipitins, etc. Some observers state that proteoses, 

 peptones, and ammo-acids, are to be found in the blood. This, 

 however, is strenuously contested by others. 



Lipoids. Fat in a very finely emulsified form and soaps are found 

 in the blood. The amount in normal human blood varies according 

 to the diet, being increased by the taking of milk or other fat. It 



