THE BLOOD 237 



per dent, in the blood of man. As to the physiologic importance or ante- 

 cedents of paraglobulin nothing is definitely known. Its constant presence 

 in the blood would indicate that it plays an equally important, though per- 

 haps different, part with serum-albumin in the nutrition of the body. 



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

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

 however, not to be 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 0.22 to 0.33 part per 

 hundred. Fibrinogen may be obtained from plasma which has been pre- 

 vented from coagulating, by the addition of magnesium sulphate in certain 

 quantities or by the addition of a saturated solution of sodium chlorid. In 

 a few minutes a flaky precipitate occurs. By repeated washing and pre- 

 cipitation with sodium-chlorid solutions of varying strength, the fibrinogen 

 may be obtained in a pure state. The history of fibrinogen is unknown, 

 though there is some experimental evidence for the belief that it is produced 

 in the liver though out of what has not been determined. Beyond the fact 

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

 knowledge either as to its origin, its nutritive value, or its final disposition in 

 the blood under normal conditions. 



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

 of fat in the form of microscopic globules. Though the percentage is nor- 

 mally not above 0.25, yet just after a meal rich in fat 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. As 

 oxidation of fat in the blood has not been established the probabilities 

 are that the microscopic granules pass across the walls of the capillaries 

 and become constituents of the lymph. Soaps or alkaline salts of the 

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

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



Sugar. The plasma also contains a small quantity of sugar in the form 

 of dextrose and is to be regarded as a normal constituent. ^ The percentage 

 of the sugar varies from o.io to 0.20 per cent. To this condition of the blood 

 in which the sugar is present in but normal amounts the term glyctmia has 

 been given. If the percentage falls below the normal amount, a. condition 

 of hypoglycemia is established; if on the contrary the percentage is increased 

 beyond the normal a condition of hyperglycemia is established, whereupon 

 the excess will be for the most part eliminated by the kidneys giving rise 

 to a condition known as glycosuria. 



If the statement be accepted that the amount of blood in a body weigh- 

 ing 70 kilos is 3864 grams (i/ipth of the body weight) the amount of sugar 

 in the entire volume of blood is at most about 7.72 grams, an amount which 

 does not materially change under physiologic conditions. 



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 accumulate beyond a small amount, since 

 they are constantly being eliminated from the blood by the various ex- 

 cretory organs. 



