ANIMAL FLUIDS AND TISSUES. 357 



Blood serum contains of water 90.5 per cent,; of solids 9.5 

 per cent., the latter being chiefly proteids 8 to 9 per cent., fats, 

 extractives, and salts from 1 to 2 per cent. Wet blood-cor- 

 puscles contain of water 54.63 per cent., haemoglobin 41.1 per 

 cent., other proteids 3.9 per cent., fats (chiefly cholesterin and 

 lecithin) 0.37 per cent. The quantity of water in corpuscles 

 varies widely, and most likely ranges in healthy blood from 76 

 to 80 per cent. 



The alkaline reaction of blood is due to the presence of acid 

 sodium carbonate, NaHCO 3 , and sodium phosphate, Na 2 HP0 4 , 

 both of which have a weak alkaline reaction. Besides these 

 alkaline salts, blood also contains others, among them chiefly 

 sodium chloride, and also the chlorides, phosphates, and sul- 

 phates of calcium, magnesium, sodium, potassium, etc. 



When blood leaves the body and is allowed to stand a while 

 (or, quicker, on shaking or agitating it violently) it separates 

 into a semisolid mass termed clot, and a pale, yellow liquid 

 termed serum, which latter, however, also solidifies after a time 

 in consequence of the coagulation of the serum-albumin. Clot 

 consists of fibrin, holding in its meshes the blood-corpuscles; 

 the latter may be removed by washing the clot in a stream of 

 water. Another method for obtaining the corpuscles is to 

 dilute mammalian blood with 10 volumes of a 2 per cent, 

 sodium chloride solution, which prevents coagulation, but allows 

 the corpuscles to settle at the bottom of the fluid. 



Fibrin exists most likely not as such in the blood, but forms 

 after it leaves the body from two kinds of albumin, termed 

 fibrinoplastic matter (identical with paraglobulin) and fibrinogen. 



Haemoglobin is the chief constituent of the red corpuscles 

 and the substance which carries oxygen to the various tissues, 

 as described in connection with the consideration of haemoglobin 

 itself. 



Examination of blood stains. Blood stains may be recognized 

 after having been washed off with as little water as possible, by 

 the following methods : 



1. Examine the reddish fluid under the microscope for blood- 

 corpuscles. 



2. Evaporate a drop of the fluid on a microscopic slide with 

 a fragment of sodium chloride, cover with a cover-glass, allow 



