THE BLOOD. 235 



obtained from serum when this fluid is saturated with magnesium 

 sulphate. As the line of saturation is approached the fluid becomes 

 turbid, and after a few minutes a fine white precipitate occurs. It 

 can then be collected on a filter, dried, and its chemic properties 

 determined. In its reactions it resembles the various members of the 

 globulin class. The amount varies from 2 to 4 per cent, in the blood 

 of man. As to the physiologic importance or antecedents of para- 

 globulin nothing is definitely known. Its constant presence in the 

 blood would indicate that it plays an equally important, though 

 perhaps different, part with serum-albumin in the nutrition of the 

 body. 



Fibrinogen. This proteid can be obtained from plasma, lymph, 

 pericardial, and peritoneal fluids, as well as from hydrocele fluid. 

 It is, however, not to _b_e_obtained from ^ serum, as it is removed from 

 the blood during the formation of solid fibrin. It is normally present 

 in the blood in very small quantity, amounting to not more than 22 

 to 33 parts per thousand. Fibrinogen may be obtained from plasma 

 which has been prevented from coagulating, by the addition of mag- 

 nesium sulphate in certain quantities or by the addition of a satu- 

 rated solution of sodium chlorid. In a few minutes a flaky precipitate 

 occurs. By repeated washing and precipitation with sodium chlorid 

 solutions of varying strength the fibrinogen may be obtained in a 

 pure state. \vThe history of fibrinogen is unknown. Beyond the fact 

 that it contributes to the formation of fibrin there is no positive 

 knowledge either as to its origin, its nutritive value, or its final dis- 

 position in the blood under normal conditions.^ 



Fat. The plasma as well as the serum contains a very small 

 quantity of fat in the form of microscopic globules. Though the 

 percentage is normally not above 0.25, yet just after a meal rich in 

 fatty matter the amount may be so great as to give to the blood 

 a milky or opalescent appearance. Within a few hours, however, 

 this excess of fat disappears from the blood, though its immediate 

 disposition is unknown. Soaps or alkaline salts of the fatty acids, 

 though formed during the digestion of fats, are not present in the 

 blood. Lecithin and cholesterin are present in very small quantities. 



Sugar .^-Sugar is present in the blood in the form of dsxtaase, 

 and is now regarded as a normal constituent// The amount is 

 about i part pgr fegusand. though it may be present to the extent 

 of 3 parts pertSousanaTBeyond this, the excess soon appears in 

 the urine. 



Extractives. The blood contains a series of nitrogenized 

 bodies, such as urea, uric acid, creatin, creatinin, xanthin, etc., which 

 result from the katabolic changes in nerve- and muscle-tissues as 

 well as from subsequent chemic combinations and decompositions. 

 Though constantly absorbed from the tissues, they seldom accumu- 



