16 THE BLOOD 



Opacity. The opacity of the blood depends on the fact that it is 

 not a homogeneous liquid, but is composed of plasma and corpuscles, 

 both of which are nearly transparent but which have each a different 

 refractive index. The rays of light, consequently, can not pass through 

 the liquid, and the mixture is opaque. 



Odor. The blood has a faint but characteristic odor. This may be 

 developed so as to be quite distinct, by the addition of a few drops of 

 sulphuric acid, when the odor peculiar to the animal from which the 

 blood has been taken becomes very marked. 



Taste. The taste of the blood is distinctly saline, on account of a 

 number of salts contained in the plasma, and particularly of a consider- 

 able proportion three to four parts per thousand of sodium chloride. 



Reaction. The reaction of the blood in health is distinctly alkaline ; 

 but it is not always easy to demonstrate this, on account of the red color 

 of the corpuscles, which obscures the reaction. If, however, a drop of 

 blood is put upon glazed reddened litmus paper and is then lightly 

 wiped off with a soft sponge, a spot remains that is of a distinctly blue 

 | color. The alkaline reaction is due to the presence of sodium carbonate 

 and sodium phosphate in the plasma. 



Specific Gravity. The specific gravity of defibrinated blood is 

 between 1.055 and 1.062, varying considerably with conditions of the 

 digestive organs. 



Temperature. The temperature of the blood usually is given as 

 between 98 and 100 Fahr. (36.67 and 37.78 C.); but experiments 

 have shown that it varies considerably in different vessels, indepen- 

 dently of exposure to external refrigerating influences. The blood is 

 warmer in the right than in the left cavities of the heart. With few 

 exceptions, it is warmer in the arteries than in the veins. It is warmer 

 in the portal vein than in the abdominal aorta. It is constantly warmer 

 in the hepatic veins than in the portal vein. The blood is warmest, 

 indeed, in the hepatic veins, where it has a temperature of 101 to 107 

 Fahr. (38.33 to 41.67 C). 



Color. The color of the blood is due to the red corpuscles. In the 

 arterial system the color is uniformly red. In the veins it usually is 

 dark blue but sometimes almost black. The color in the veins, however, 

 is not constant. Many years ago, John Hunter observed, in a case of 

 syncope, that the blood obtained by venesection was bright red. The 

 color of the venous blood depends on the condition of the organ or 

 part from which it is returned. The red color of venous blood was first 

 noticed by Bernard in the renal veins, where it contrasts strongly with 

 the black blood in the ascending vena cava. When the excito-secretory 

 nerve of the submaxillary gland is faradized, the blood coming from the 



