LOCAL VARIATIONS. 



353 



Fig. 125. 



On the other hand, the venous blood coming from the muscular tissue 

 is very dark colored, especially if the muscles be in a state of active 

 contraction. As the muscles form so 

 large a part of the entire mass of the 

 body, their condition has a prepondera- 

 ting influence upon the color of the 

 venous blood in general. The greater 

 the activity of the muscular system, the 

 darker is the color of the blood return- 

 ing from the trunk and extremities. 

 When the muscles are in a state of re- 

 pose or paralysis, on the contrary, the 

 change is less marked ; and in the com- 

 plete relaxation produced by abundant 

 hemorrhage or by complete etherization, 

 the blood in the veins often approxi- 

 mates in color to that in the arteries. 



Finally, in the lungs the reverse pro- 

 cess takes place. In these organs the 

 blood is supplied with a fresh quantity 

 of oxygen, to replace that which has 

 been consumed elsewhere ; and accord- 

 ingly it changes its color from dark 

 purple to bright red as it passes through 

 the pulmonary capillaries. 



Both the physical and chemical phe- 

 nomena, therefore, of the circulation 

 vary at different times and in different 

 organs. The actions which go on 

 throughout the body, are varied in cha- 

 racter, and produce a similar difference 

 in the phenomena of the circulation. 

 The venous blood, consequently, has a 

 different composition as it returns from 

 different organs. In the parotid gland 

 it yields the ingredients of the saliva ; 

 in the kidneys those of the urine. In 

 the intestine it absorbs the nutritious 

 elements of the digested food ; and in 

 the liver it gives up substances destined 

 to produce the bile, while it absorbs 

 glucose from the hepatic tissue. In the 

 lungs it changes from blue to red, and 

 in the capillaries of the general system, 

 from red to blue ; and its temperature, also, varies in different veins, 

 according to the peculiar chemical and nutritive changes going on in the 

 organs from which they originate. 



DIAGRAM OF THK CIRCULA- 

 TION. 1. Heart. 2. Lungs. 3. Head 

 and upper extremities. 4 Spleen. 6. 

 Intestine. 6. Kidney. 7. Lower ex- 

 tremities. 8. Liver. 



