352 THE CIRCULATION. 



by Bernard 1 in the submaxillary gland of the dog. During the ordinary 

 condition of glandular repose he found that it required sixty-five seconds 

 to obtain five cubic centimetres of blood from the submaxillary vein ; 

 but, when the gland was excited to functional activity, the same quan- 

 tity of blood was discharged by the vein in fifteen seconds. Thus the 

 volume of blood passing through the organ in a given time was more 

 than four times as great while the gland was in a state of active secre- 

 tion, as in a condition of repose. 



The increased flow of blood, in a secreting gland, is accompanied also 

 by an important change in its appearance. During repose, the blood, 

 which enters the submaxillary gland from the arteries bright red, is 

 changed in its tissue from arterial to venous, and passes out by the 

 veins of a dark color. But when the secretion of the gland is excited, 

 either by galvanization of its nerve or by introducing vinegar into the 

 mouth of the animal, the blood is not only discharged in larger quantity, 

 but passes out red by the veins, so as hardly to be distinguished in 

 color from arterial blood. When the secretion of the gland is suspended, 

 the blood in its vein again becomes dark-colored as before. There is 

 little doubt that the same is true of most of the secreting glands, and 

 that the blood circulating in their capillaries is changed from red to blue 

 only during the period of functional repose ; while at the time of active 

 secretion it not only passes through the vessels in greater abundance, 

 but also retains its ruddy color in the veins. 



This -is because, during the period of glandular repose, the blood per- 

 forms in its tissues the usual functions of nutrition. It therefore under- 

 goes the ordinary changes and becomes altered in color from arterial to 

 venous. But the period of active secretion is a period of congestion, 

 during which the blood passes in larger quantity, while its watery and 

 saline ingredients exude into the secretory ducts, bringing with them 

 the materials accumulated in the interval of repose. There is nothing 

 in this process to exhaust the oxygen of the blood or to change its 

 color from arterial to venous, and it therefore passes into the veins 

 comparatively unaltered. 



A similar ruddy color of venous blood is to be seen in the renal veins, 

 where it is often nearly identical with that of arterial blood. The dif- 

 ference in hue between the renal veins and the neighboring muscular 

 veins or the vena cava, when exposed by opening the abdomen of the 

 living animal, is very marked, provided the kidneys be at the time in a 

 state of functional activity. The greater part of the blood traversing 

 these organs is changed only by the elimination of its urea and the 

 remaining ingredients of the urine, which exude into the excretory 

 tubules. The process of active local nutrition is here altogether sub- 

 servient to the discharge of organic materials already existing in the 

 blood; -and the loss of oxygen and alteration in color of the circulating 

 fluid are thus comparatively insignificant. 



1 Leqons sur les Liquides de TOrganisme. Paris, 1859, tome ii. p. 272. 



