CHEMICAL COMPOSITION OF BLOOD-PLASMA. 447 



Its percentage composition, according to Michel, is as follows: 

 C, 53.08; H, 7.10; N, 15.93; S, 1.90; 0, 21.96. 



Its molecular composition, according to Schmiedeberg,* may be 

 represented by C78HJ22N20SO24 or some multiple of this formula. 

 Serum-albumin shows the general reactions of the native albumins. 

 One of its most useful reactions is its behavior toward magnesium 

 sulphate and ammonium sulphate. .Serum-albumin usually occurs in 

 the body-liquids together with the globulins, as is the case in blood. 

 If such a liquid is thoroughly saturated with solid magnesium sul- 

 phate or half saturated with ammonium sulphate, the globulins 

 are precipitated completely, while the albumin is not affected. 

 So far as the blood and similar liquids are concerned, a definition 

 of serum-albumin might be given by saying that it comprises all 

 the proteins not precipitated by saturation with magnesium sul- 

 phate or by half saturation with ammonium sulphate. When its 

 solutions have a neutral or an acid reaction, serum-albumin is 

 precipitated in an insoluble form by heating the solution above a 

 certain degree. Precipitates produced in this way by heating 

 solutions of proteins are spoken of as coagulations — heat coagula- 

 tions — and the exact temperature at which coagulation occurs 

 is to a certain extent characteristic for each protein. The tem- 

 perature of coagulation of serum-albumin is usually given at from 

 70° to 75° C, but it varies greatly with the conditions, — for in- 

 stance, with the reaction of the solution, its concentration in salts, 

 or with the nature of the salts present. It has been asserted, 

 in fact, that careful heating under proper conditions gives separate 

 coagulations at three different temperatures, — namely, 73°, 77°, 

 and 84° C, — indicating the possibility that what is called "serum- 

 albumin" may be a mixture of three proteins. Serum-albumin 

 occurs in blood-plasma and blood-serum, in lymph, and in the 

 different normal and pathological exudations found in the body, 

 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. 



ParaglobuUn, which belongs to the group of globulins, exhibits 

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

 it is completely precipitated from its solution by saturation with 

 magnesium sulphate or by half-saturation with ammonium sul- 

 phate. 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; 0, 23.32. Schmiedeberg 

 gives it a molecular composition corresponding to the formula 

 * "Archiv f. exper. Pathol, u. Pharmakol.," 39, 1, 1897. 



