CHEMICAL COMPOSITION OF BLOOD-PLASMA. 423 



such as pericardial liquid, hydrocele fluid, etc. The amount of 

 serum-albumin in the blood varies in different animals, ranging 

 among the mammalia 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 proteins of the food. It is known that 

 protein 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 proteins of an entirely different char- 

 acter, namely, peptones and proteoses, or, indeed, 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 stand- 

 point serum-albumin is often considered to be the main source of 

 protein 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 

 protein 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 

 Cii 7 H 182 N 30 S0 38 + JH 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 protein is 



