338 



OF THE CIRCULATION OF THE BLOOD. 



The periodic variations of the blood-pressure depend essentially on the fre- 

 quency and vigor of the contractions of the heart. When the heart beats 



slowly and strongly the ten- 



Fic - 142 - sion of the Arteries varies 



greatly between systole and 

 diastole, and the maxima and 

 minima of the pressure repre- 

 sented by the height of the 

 curves differ considerably 

 from the mean pressure, and 

 the pulse may become percep- 

 tible even in the capillaries. 

 When the cardiac beats are 

 frequent, on the other hand, 

 the maxima and minima of 

 the pressure differ but little 

 from the mean pressure; the 

 curves are smaller and more 

 numerous, and the mean pres- 

 sure is relatively high. These 

 conditions may be induced at 

 will through the Vagus; mod- 

 erate stimulation of this nerve 

 causing slow pulse with wide 

 excursions of the tracings and 



Pick's Spring Kymograph: A,C-spring; B u, support; c, l w . m eail pressure, whilst 

 rod which communicates the movements of the spring to the section ()f the Uerve Causes 

 lever D, and thus to the writing-needle G, the vertically of quicker pulse with smaller 



excursions and higher mean 

 pressure. Fick, 1 from experi- 

 ments made on the dog, with 



his modified spring manometer (Fig. 142), found the pressure in the right 

 auricle nil (= atmospheric pressure) ; during inspiration it sank to 10 mm. of 

 mercury below zero. In the right ventricle the pressure varied from 18-42 



mm., and in the left ventricle the maximum was 

 FIG. 143. 140 mm. The pressure of the blood in the aorta 



rose as high during the period of systole as in 

 the ventricle, but it did not fall so low during 

 the diastole. Badoud,' 2 working under Fick 

 and using his C-spring manometer, found the 

 pressure of the blood in the pulmonary artery 

 constantly below 60 mm. of mercury ; after sec- 



Normal arterial tracing obtained tion of tne s P inal c ' orfl . 5t fel1 considerably, and 

 with the spring Kymograph; dog whcu the cord was stimulated electrically, it not 

 under Cm-am. only rose, as occurs in th e systemic arteries, but 



rose considerably above the normal, this being 



due to the muscular contraction excited in the body generally. AVorm Miiller 3 

 has shown that when the tension of the vascular system has been lowered by 

 the section of the spinal cord and cardiac nerves, the blood-pressure cannot 

 again be raised to its normal height by the injection of blood into the ves- 

 sels. He also showed that blood to the extent of two per cent, of the body 



the movement of which is secured by the second rod E; I?, 

 leaden tulie by which the cavity of the spring is in commu- 

 nication with the arterv. 



1 Yorliand. d. WuTv.hnru Pliys.-Mod. Ges., Bel. iv, 1873, p. 2'2'.}. 



2 Imui^. Dissert , Wiirzburg, 1874. 



3 Sitz.-l>cr. d. Sachs. Ges. d. Wiss., 1873, p. 57:1. 



