196 DISTRIBUTION OF THE BLOOD. 



Fig. 86, 2-8, are curves of the pulse in the common jugular vein (after Friedreich). 

 Although at first sight the curves appear to be very different, they all agree in this, 

 that the various events occurring in the heart during a cardiac revolution are 

 indicated more or less completely. In all the curves, a, b = auricular contraction. 

 The auricle, when it contracts, excites a positive wave in the veins (Gendrin, 1843, 

 Marey, Friedreich). The elevation, &, c, is caused by the large blood-wave 

 produced in the veins, owing to the emptying of the ventricle. It is always greater, 

 of course, in insufficiency of the tricuspid valves than under normal circumstances 

 (Fig. 86, 9 and 10). In the latter case, the closure of the tricuspid valve causes only 

 a slight wave-motion in the auricle. The apex, c, of this wave may be higher or 

 lower, according to the tension in the vein and the pressure exerted by the sphygmo- 

 graph. As a general rule, at least one notch (4, 5, 6, e) follows the apex, due to 

 the prompt closure of the valves of the pulmonary artery. The closure of the 

 closely adjacent aortic valves may cause a small secondary wave near to c (as in 1 

 and 2, d). The curve falls towards f, corresponding to the diastole of the heart. 



A well-marked venous pulse occurs when the right auricle is greatly 

 congested, as in cases of insufficiency of the mitral valve or stenosis of 

 the same orifice. In rare cases, in addition to the pulse in the common 

 jugular vein, the external jugular, the facial, thyroid, external thoracic 

 veins, or even the veins of the upper and lower extremities may 

 pulsate. 



A similar pulsation must occur in the pulmonary veins in mitral 

 insufficiency, but of course the result is not visible. 



On rare occasions, a pulse occurs in the veins on the back of the 

 hand and foot, owing to the arterial pulse being propagated through the 

 capillaries into the veins. This may occur under normal circumstances, 

 when the peripheral ends of the arteries become dilated and relaxed 

 (Quincke), or when the blood-pressure within these vessels rises rapidly 

 and falls as suddenly, as in insufficiency of the aortic valves. 



In progressive effusion into the pericardium, at first the carotid pulse becomes 

 smaller and the venous pulse larger; beyond a certain pressure, the latter ceases 

 (Riegel). 



100, Distribution of the Blood. 



Methods. The methods adopted do not give exact results. J. Ranke ligatured 

 the parts during life, removed them, and investigated the amount of blood while 

 the tissues were still warm. 



In a rabbit, one-fourth of the total amount of the blood is found in 

 each of the following : a, in the passive muscles ; b, in the liver ; c, in 

 the organs of the circulation (heart and great vessels) ; d, in all other 

 parts together (J. Eanke). 



The amount of blood is influenced by (1) The anatomical distribution (vascularity 

 or the reverse) of the vessels as a whole ; (2) the diameter of the vessels, which 

 depends upon physiological causes (a) on the blood-pressure within the vessels ; 

 (b) on the condition of the vaso-motor or vaso-dilatator nerves ; (c) on the condition 

 of the tissues themselves, e.g., the vessels of the intestine during absorption; by the 

 vessels of muscle during muscular contraction ; of vessels in inflamed parts. 



