THE BLOOD. 79 



a. Water. The water of the serum varies in amount according to 

 the amount of food, drink, and exercise, and with many other circum- 

 stances. 



b. Proteids. a. Serum-albumin is the chief proteid found in serum. 

 The proportion which it bears to paraglobulin, the other proteid, is as 

 1.011 to 1. in human blood. 



Serum-albumin has been shown by Halliburton to be a compound 

 body, which may be called serine, made up of three proteid s, which co- 

 agulate at different temperatures, <*at 73 C., fi at 77 C., and y at 85 0. 

 The serine is entirely coagulated at 94 C., and also by the addition of 

 strong acids, such as nitric and hydrochloric ; by long contact with al- 

 'cohol it is precipitated. It is not precipitated on addition of ether, and 

 so differs from the other native albumin, viz., egg-albumin. When dried 

 at 104 F. (40 C.) serum-albumin is a brittle, yellowish substance, solu- 

 ble in water, possessing a laevorotary power of 56. It is with great 

 difficulty freed from its salts, and is precipitated by solutions of metallic 

 salts, e.g., of mercuric chloride, copper sulphate, lead acetate, sodium 

 tungstate, etc. If dried at a temperature over 35 C. the residue is insol- 

 uble in water, having been changed into coagulated proteid. Serum- 

 albumin may be precipitated from serum, from which the paraglobulin 

 has been previously separated by saturation with magnesium sulphate, 

 and removed by filtration, by further saturation with sodium sulphate, 

 sodium nitrate, or iodide of potassium. 



fi. Paraglobulin can be obtained as a white precipitate from cold serum 

 by adding a considerable excess of water, and passing through the mix- 

 ture a current of carbonic acid gas or by the cautious addition of dilute 

 acetic acid. It can also be obtained by saturating serum with either 

 crystallized magnesium sulphate, or sodium chloride, nitrate, acetate, or 

 carbonate. When obtained in the latter way, precipitation seems to be 

 much more complete than. by means of the former method. Paraglobu- 

 lin belongs to the class of proteids called globulins. 



c. The salts of sodium predominate in serum as in plasma, and of 

 these the chloride generally forms by far the largest proportion. 



d. Fats are present partly as fatty acids and partly emulsified. The 

 fats are tri-olein, tri-stearin, tri-palmitin. The amount of fatty matter 

 varies according to the time after, and the ingredients of, a meal. Of 

 cholesterin and lecithin there are mere traces. 



e. Grape sugar is found principally in the blood of the hepatic vein, 

 about one part in a thousand. 



f. The extractives vary from time to time ; sometimes uric and hip- 

 puric acids are found in addition to urea, kreatin, and kreatinin. Urea 

 exists in proportion from .02 to .04 per cent. 



g. The yellow pigment of the serum and the odorous matter which 

 gives the blood of each particular animal a peculiar smell, have not 

 yet been exactly differentiated. The former is probably choletelin 

 {MacMunn). 



