304 



FUNCTIONS OF NUTRITION. 



Local Variations in the Capillary Circulation, 



An important class of phenomena connected with the capillary cir- 

 culation consists of its local variations. These variations are often 



very marked, and show themselves in 

 many different parts of the body. The 

 pallor or suffusion of the face from men- 

 tal emotion, the congestion of the glands 

 and mucous membranes during diges- 

 tion, and the denned redness of the skin 

 after irritating applications, are instances 

 of this kind. They are due to the vary- 

 ing condition of the smaller arterial 

 branches which contract or dilate after 

 different nervous influences, and thus 

 diminish or increase the quantity of 

 blood in the capillary circulation. When 

 contracted, they resist the impulse of the 

 arterial current, and admit the blood in 

 smaller quantity. When dilated, they 

 allow it a free access, and the blood 

 passes in greater abundance to the 

 capillary vessels. 



These changes are most distinctly 

 manifested in the periodical congestion 

 of the glandular organs. All the glands 

 and mucous membranes of the digestive 

 apparatus enter into a state of vascular 

 excitement at the time of secretion and 

 digestion. This unusual vascularity can 

 be seen, in the living animal, in the 

 pancreas, and in the mucous membranes 

 of the . stomach and small intestine ; 

 which are visibly redder and more turgid 

 during digestion and absorption than in 

 the fasting condition. 



The variations of the capillary circu- 

 lation, as influenced by glandular activ- 

 ity and repose, have been most success- 

 fully studied in the submaxillary gland 

 of the dog. While this gland is in ac- 

 tive secretion the quantity of blood pass- 

 ing through its vessels is largely in- 

 creased. In the experiments of Ber- 

 nard* the submaxillary vein, during 

 the condition of glandular repose, yielded 

 five cubic centimetres of blood in a little more than one minute ; but 



DIAGRAM OF THE CIRCULATION. 1. 

 Heart. 2. Lungs. 3. Head and upper 

 extremities. 4. Spleen. 5. Intestine. 

 6. Kidney. 7. Lower extremities. 8. 

 Liver. 



* Legons sur les Liquides de 1'Organisrae. Paris, 1859, tome ii., p. 272 



