78 HANDBOOK OF PHYSIOLOGY. 



The chief methods of obtaining plasma free from corpuscles are : 

 (1) by cold, the temperature should be about C. and may be two or 

 three degrees higher, but not lower. (2) The addition of neutral salts, 

 in certain proportions, either solid or in solution, e. g. 9 of sodium sul- 

 phate, if solid, 1 part to 12 parts of blood; if a saturated solution, 1 part 

 to 6 parts of blood; of magnesium sulphate, of a 23$, or if saturated 

 .solution 1 part to 4 of blood. (3) A third way is to mix frog's blood 

 with an equal part of a 5f of cane sugar, and to get rid of the corpuscles 

 by nitration; or (4) by the injection of peptone into the veins of mam- 

 mals, previous to bleeding them to death, and afterwards subjecting the 

 plasma thus obtained to the action of a centrifugal machine. 



Salts of the plasma. In 1000 parts of the plasma there are: 



Sodium chloride, 5.546 



Soda, 1.532 



Sodium phosphate, ...... .271 



Potassium chloride, . .... .359 



" sulphate, . . . . . .281 



Calcium phosphate, .298 



Magnesium phosphate, 218 



8.505 



(2.) Chemical Composition of Serum. The serum is the liquid 

 part of the blood or of the plasma remaining after the separation of the 

 clot. It is an alkaline, yellowish, transparent fluid, with a specific 

 gravity of from 1025 to 1032. In the usual mode of coagulation, part 

 of the serum remains in the clot, and the rest, squeezed from the clot 

 by its contraction, lies around it. Since the contraction of the clot may 

 continue for thirty-six or more hours, the quantity of serum in the 

 blood cannot be even roughly estimated till this period has elapsed. 

 There is nearly as much, by weight, of serum as there is clot in coagu- 

 lated blood. 



Serum may be obtained from blood corpuscles by allowing blood to 

 clot in large test tubes, and subjecting the test tubes to the action of a 

 centrifugal machine for some time. 



In tabular form the composition may be thus summarized. In 1000 

 parts of serum there are: 



Water, about 900 



Proteids : 



a. Serum-albumin, . . . . . I en 



ft. Paraglobulin, f 



Salts. 



Fats including fatty acids, cholesterin, lecithin ; and ^ 

 some soaps, ....... 



Grape sugar in small amount, ..... 



Extractives kreatin, kreatinin, urea, etc., . 

 Yellow pigment, which is independent of haemoglobin, 

 Gases small amounts of oxygen, nitrogen, and car- 

 bonic acid, 



1000 



