COLOR OF THE BLOOD. 5 



what less in the female than in the male. Its density varies greatly under different con- 

 ditions of digestion. 



Temperature. The temperature of the blood is generally given as from 98 to 100 

 Fahr. ; but recent experiments have shown that it varies considerably in different parts 

 of the circulatory systsm, independently of exposure to the refrigerating influence of the 

 atmosphere. By the use of very delicate registering thermometers, Bernard has suc- 

 ceeded in establishing 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, indepen- 

 dently 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 

 from 101 to 107. In the aorta, it ranged from 99 to 105. 



"We may assume, then, in general terms, that the temperature of the blood in the 

 deeper vessels is from 100 to 107 Fahrenheit. 



Color of the Blood. 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 sometimes almost 

 black. This difference in color between the blood in the arterial and in the venous sys- 

 tem was a matter of controversy at the time of Harvey. By the discoverer of the cir- 

 culation, the difference, which is now universally known and admitted as regards most 

 of the veins, was supposed to be merely accidental and dependent on external causes. 

 Fifty years later, Lower demonstrated the change of color in the blood as it passes 

 through the lungs, and associated it with the true cause ; viz., the absorption of oxygen. 

 The color in the veins, however, is not constant. Many years ago, John Hunter ob- 

 served, 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 no- 

 ticed 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 only existed during the 

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

 was arrested, the blood became dark. He was led, from this observation, to examine 

 the venous blood from other glands ; and, directing his attention to those which he was 

 able to examine during their functional activity, particularly the salivary glands, he found 

 the blood red in the veins during secretion, but becoming dark as soon as secretion was 

 arrested. These observations may be easily verified by opening the abdomen of a living 

 animal, exposing the renal veins, and introducing a canula into the ureter, so as to 

 be able to note the flow or arrest of the urine. So long as the urine continues to flow, 

 the blood in these vessels is bright red ; but when secretion becomes arrested, as it soon 

 does after exposure of the organs, it presents no difference from the blood in the 

 vena cava. In the submaxillary gland, by the galvanization of a certain nerve which he 

 calls the motor nerve of the gland, Bernard has been able to produce secretion, and, by 

 the galvanization of another nerve, to arrest it ; in this way changing at will the color 

 of the blood in the vein. It has J>een found by the same observer that division of the 

 sympathetic in the neck, which dilates the vessels and increases the supply of blood to 

 one side of the head, produces a red color of the blood in the jugular. He has also 

 found that paralysis of a member by division of the nerve has the same effect on the 

 blood returning by the veins. 



The explanation of these facts is evident when we reflect upon the reasons why the 

 blood is red in the arteries and dark in the veins. Its color depends upon the corpus- 

 cles ; and as the blood passes through the lungs it loses carbonic acid and gains oxygen, 



