170 PHYSIOLOGY. 



noted. A cannula is placed in the animal's carotid through which 

 is extracted a quantity of blood to serve as a sample. This is 

 defibrinated, whereupon portions of it are diluted at different known 

 strengths. The remainder of the blood in the body is then allowed 

 to escape, and is collected and defibrinated. A normal salt solution 

 is next run through the vessels and likewise collected. The entire 

 body, minus the stomach and intestines, is then cut into very fine 

 pieces and extracted with water for one or two days, at the end of 

 which time the bloody water is expressed and added to the drawn 

 blood and washings. The entire amount is carefully measured. 



The experimenter compares this diluted blood with the pre- 

 viously prepared samples of the diluted blood of known strength 

 until he finds tints of two that are exactly alike. From the total 

 quantity of diluted blood and the knowledge of what the sample 

 contains it is comparatively easy to calculate the amount of blood 

 contained in the body. To this must be added the blood drawn at 

 first to make the various samples. The weight of the animal com- 

 pared with the above results gives the proportionate amount. 



By this and similar computations it has been ascertained that 

 the blood is equal to from one-eleventh to one-fourteenth of the 

 bodyweight. Approximately, it may be said to be one-thirteenth of 

 the bodyweight. 



"Boughly, it may be said that the lungs, heart, large arteries, 

 and veins contain one-fourth; the muscles of the skeleton one-fourth; 

 the liver one-fourth; and other organs one-fourth.'' (Ranke.) 



The quantity of blood is a variable quantity. It is more abun- 

 dant during absorption of the digestive products than in fasting. It 

 has been experimentally proven that during digestion the lethal dose 

 of strychnia must be double that in an animal fasting. Diarrhoea 

 and sweats diminish the quantity of blood. The viscera contain the 

 most blood; the muscles contain much less. The quantity of blood 

 in an or^an varies with its activity or repose. The salivary glands 

 when active receive four times more blood than when in repose. 



Arterial and Venous Blood Compared. At this point the stu- 

 dent's attention is called to a few main points wherein the arte- 

 rial and venous bloods differ. Very conspicuously stands out the 

 marked difference in color: the scarlet of arterial, the bluish red of 

 venous blood. These color-differences depend primarily upon the 

 amount of oxygen-gas contained in the blood. It unites with the 

 iron of the blood-corpuscles (little bodies) to form a very unstable 

 compound, known as oxyha3moglobin. Whe'n carbon-dioxide gas is 



