PHYSICAL PROPERTIES OF BLOOD. 269 



the fluid portion of the blood the blood is said to be lakey. This 

 solution of the hemoglobin may be brought about in many ways, 

 as by adding distilled water or a solution of sodium chlorid or 

 other neutral salt, provided that the solution is not isotonic. An 

 isotonic solution is one in which the amount of the salt present 

 does not change the form of the red corpuscles or dissolve out its 

 coloring-matter. In the case of sodium chlorid, this is for human 

 blood a solution having a percentage of 0.9. 



Reaction of Blood. The alkalinity of blood is a property essen- 

 tial to life, and, so far as the plasma is concerned, depends upon 

 the presence of sodium carbonate and phosphate. The alkalinity 

 is not always the same ; it is least in the morning, increases in the 

 afternoon, and diminishes at night. It increases during digestion 

 and after muscular exercise. It is said that the blood becomes 

 acid immediately before death in cases of cholera, and also in the 

 condition of unconsciousness called coma, which occurs sometimes 

 in diabetes. 



Odor of Blood. Blood has an odor which is said to be charac- 

 teristic of the species of animal from which it is taken. The odor 

 is usually very slight, but it may be intensified by the addition of 

 sulphuric acid. 



Taste of Blood. The sodium chlorid which blood contains gives 

 to it a salty taste. 



Quantity of Blood. The amount of blood in the body of a 

 human adult is about 7.7 per cent., one-thirteenth of his weight ; 

 some authorities state one-eighth, and others one-fourteenth. In 

 a newborn child it is about one-nineteenth. During the latter 

 half of the period of pregnancy it is increased, and it is also in- 

 creased during digestion. 



There are various methods of determining the quantity of 

 blood in the body ; that of Welcker is, perhaps, the best known. 

 It consists in opening a vein of an animal and withdrawing blood, 

 which is measured and defibrinated. This is then divided into 

 portions, each of which is diluted with a different amount of 

 water, which thus gives solutions of different colors ; these 

 serve subsequently as standards of comparison. The animal is 

 then bled until all the blood that will flow has been withdrawn ; 

 this is defibrinated, and sufficient salt solution is injected into the 

 vessels to wash out the blood that remains. This is continued 

 until the fluid comes out colorless. The body is then cut up into 

 small pieces and mixed with saline solution, and this then filtered, 

 and the filtrate, together with the washings of the blood-vessels, is 

 added to the defibrinated blood. The mixture is measured, and 

 diluted with water until its color corresponds with that of one of 

 the standard solutions, when the calculation can be made which 

 will determine the total amount of blood in the body. It is 

 necessary, of course, to include the quantity of blood which was 

 first withdrawn to make the standard solutions. 



