130 HANDBOOK OF PHYSIOLOGY. 



high altitudes. According to Jones it is very high (1.066) in new-born 

 infants, but, after the second week, sinks throughout the first year of 

 life (to 1.048-1.050) and then rises again, becoming almost as high in old 

 age as in infancy. In pathological conditions the variations may be 

 most marked, e.g., the specific gravity is constantly lowered in ana?mia, 

 while in cachexia resulting from malignant new growths it may even be 

 reduced to 1.030 (Lyonnet). Various drugs (e.g., diuretics and dia- 

 phoretics) also affect the specific gravity. A rapid and useful method 

 of estimating the specific gravity of blood is the one devised by Hammer- 

 schlag as a modification of Boy's method. Chloroform and benzol, 

 which are respectively heavier and lighter than blood, are mixed in such 

 proportions that the resultant specific gravity is about 1.059. A drop of 

 blood is then added to this mixture, with which it does not mix at all, 

 "but floats as a red bead. Accordingly as it sinks to the bottom or rises 

 to the top, either chloroform or benzol is added. When the drop re- 

 mains stationary in the body of the liquid the specific gravity of the 

 mixture will be the same as that of the blood, and can be ascertained by 

 a hydrometer. The reaction of blood is faintly alkaline and the taste 

 saltish. Its temperature varies slightly, the average being 37.8 C. (100 

 F.). The blood stream is warmed by passing through the muscles, 

 nerve centres, and glands, but is somewhat cooled on traversing the 

 capillaries of the skin. Recently drawn blood has a distinct odor, which 

 in many cases is characteristic of the animal from which it has been 

 taken. It may be further developed also by adding to blood a mixture 

 of equal parts of sulphuric acid and water. 



Quantity of the Blood. The quantity of blood in any animal 

 under normal conditions bears a fairly constant relation to the body- 

 weight. The methods employed for estimating it are not so simple as 

 might at first sight have been thought For example,, it would not be 

 possible to get any accurate information on the point from the amount 

 obtained by rapidly bleeding an animal to death, for then an indefinite 

 quantity would remain in the vessels, as well as in the tissues; nor, on 

 the other hand, would it be possible to obtain a correct estimate by less 

 rapid bleeding, as, since life would be more prolonged, time would be 

 allowed for the passage into the blood of lymph from the lymphatic 

 vessels and from the tissues. In the former case, therefore, we should 

 under-estimate, and in the latter over-estimate the total amount of the 

 blood. 



Of the several methods which have been employed, the most accurate 

 appears to be the following. A small quantity of blood is taken from 

 an animal by venesection; it is defibrinated and measured, and used to 

 make standard solutions of blood. The animal is then rapidly bled to 

 death, and the blood which escapes is collected. The blood-vessels are 

 next washed out with saline solution until the washings are no longer 



