CHEMICAL COMPOSITION OF BLOOD-PLASMA. 411 



icardial liquid, hydrocele fluid, etc. The amount of serum-albumin 

 in the blood varies in different animals, ranging among the mam- 

 malia from 2.67 per cent, in the horse to 4.52 per cent, in man. In 

 some of the cold-blooded animals it occurs in surprisingly small 

 quantities, 0.36 to 0.69 per cent. As to the source or origin of 

 serum-albumin, it is frequently stated that it comes from the digested 

 proteids of the food. It is known that proteid material in the food 

 is not changed at once to serum-albumin during the act of digestion; 

 indeed, it is known that the final products of digestion are a group of 

 proteids of an entirely different character, namely, peptones and 

 proteoses, or possibly a series of much simpler split products; but 

 during the act of absorption into the blood these latter bodies have 

 been supposed to undergo transformation into serum-albumin. From 

 a physiological standpoint serum-albumin is often considered to be 

 the main source of proteid nourishment for the tissues generally. 

 As will be explained in the section on Nutrition, one of the most 

 important requisites in the nutrition of the cells of the body is an 

 adequate supply of proteid material to replace that used up in the 

 chemical changes, the metabolism, of the tissues. Serum-albumin 

 has been supposed to furnish a part, at least, of this supply, 

 although, as a matter of fact, there is no substantial proof that this 

 view is correct. As long as the serum-albumin is in the blood- 

 vessels it is, of course, cut off from the tissues. The cells, however, 

 are bathed directly in lymph, and this in turn is formed from the 

 plasma of the blood which is transuded, or, according to some 

 physiologists, secreted, through the vessel walls. 



Paraglobulin, which belongs to the group of globulins, exhibits 

 the general reactions characteristic of the group. As stated above, 

 it is completely precipitated from its solutions by saturation with 

 magnesium sulphate or by half saturation with ammonium sulphate. 

 It is incompletely precipitated by saturation with common salt 

 (NaCl). In neutral or feebly acid solutions it coagulates upon 

 heating to 75 C. Hammarsten gives its percentage composition 

 as: C, 52.71; H, 7.01; N, 15.85; S, 1.11; O, 23.32. Schmiedeberg 

 gives it a molecular composition corresponding to the formula 

 Cii7H 182 N so SO S8 + iH 2 O. According to Faust, the precipitate of 

 paraglobulin usually obtained with magnesium sulphate contains a 

 certain amount of an albuminoid body, glutolin, which he believes 

 to be a constant constituent of blood-plasma. Paraglobulin occurs 

 in blood, in lymph, and in the normal and pathological exudations. 

 The amount of paraglobulin present in blood varies in different 

 animals. Among the mammalia the amount ranges from 1.78 per 

 cent, in rabbits to 4.56 per cent, in the horse. In human blood it is 

 given at 3.10 per cent., being less in amount, therefore, than the 

 serum-albumin. It is usually stated that more of this proteid is 



