4: THE BLOOD. 



considerable proportion, three or four parts per thousand, of sodium chloride 

 in the plasma. 



The reaction of the blood is always distinctly alkaline. It is not easy, 

 however, to demonstrate the alkalinity of the blood, on account of the red 

 color of the blood-corpuscles; but the difficulty may be avoided by using 

 certain precautions. The following method, employed by Schiifer, is quite 

 satisfactory : A drop of blood is put upon a piece of glazed, reddened litmus- 

 paper. After a few seconds the blood is lightly wiped off with a damp cloth, 

 leaving a spot of a distinctly blue color. According to Zuntz, the alkalinity 

 diminishes rapidly after the blood is drawn from the vessels. The alkaline 

 reaction is due to the presence of sodium carbonate and sodium phosphate in 

 the plasma. 



The specific gravity of defibrinated blood is between 1052 and 1057 

 (Robin), being somewhat less in the female than in the male. The density 

 varies greatly under different conditions of digestion. 



Temperature. The temperature of the blood is generally given as between 

 98 and 100 Fahr. (36-67 and 37'78 C.) ; but experiments have shown that 

 it varies considerably in different parts of the circulatory system, independ- 

 ently of exposure to the refrigerating influence of the atmosphere. By the 

 use of very delicate registering thermometers, Bernard succeeded in estab- 

 lishing the following facts with regard to the temperature in various parts of 

 the circulatory system, in dogs and sheep : 



1. The blood is* warmer in the right than in the left cavities of the heart. 



2. It is warmer in the arteries than in the veins, with a few exceptions. 



3. It is generally warmer in the portal vein than in the abdominal aorta, 

 independently of the digestive act. 



4. It is constantly warmer in the hepatic than in the portal veins. 



He found the highest temperature in the blood of the hepatic vein, where 

 it ranged between 101 and 107 Fahr. (38-33 and 41-67 C.). In the aorta, 

 it ranged between 99 and 105 Fahr. (37'22 and 40-55 C.). It may be 

 assumed, then, in general terms, that the temperature of the blood in the 

 deeper vessels is between 100 and 107 Fahr. (37-78 and 41-67 C.). 



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

 system it is uniformly red. In the veins it is generally dark blue and some- 

 times 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 drawn 

 by venesection was bright red ; and more recently, Bernard has demonstrated 

 that in some veins, the blood is nearly if not quite as red as in the arterial 

 system. The color of the venous blood depends upon the condition of the 

 organ or part from which it is returned. The red color was first noticed by 

 Bernard in the renal veins, where it contrasts very strongly with the black 

 blood in the vena cava. He afterward observed that the redness existed only 

 during the activity of the kidneys ; and when, from any cause, the secretion 

 of urine was arrested, the blood became dark. He was led, from this obser- 

 vation, to examine the venous blood from other glands ; and directing his 

 attention to those which he was able to examine during their activity, par- 



