504 CIRCULATION OF BLOOD AND LYMPH. 



increased output of blood from the heart. Observations with the 

 sphygmomanometer show that after full meals there is a marked 

 increase in the pulse pressure, indicating a more effective beat of the 

 heart. So far as the effect on the heart is concerned, the result of a 

 meal is similar to that of muscular exercise, and this reaction may 

 account for the fact, not infrequently observed, that in elderly 

 people whose arteries are rigid an apoplectic stroke may follow a 

 heavy meal. 



The Method of Determining Venous Pressures and Capillary 

 Pressures in Man. — A number of methods have been proposed 

 for determining venous pressures in man, the simplest being 

 that described by Gaertner.* It consists simply in raising 

 slowly the extended arm of the patient until the veins on the back 

 of the hand just disappear. The height above the heart at which 

 this occurs gives the venous pressure in the right auricle, since the 

 vein may be considered as a manometer tube ending in the auricle. 

 In this and in other methods of measuring venous pressures, and 

 the same is true, of course, of arterial and capillary pressures, 

 there must be some agreement as to what constitutes the heart 

 level, since the highest and lowest points of the heart when 

 the individual is standing or sitting may differ by as much as 15 

 centimeters. Von Recklinghausen proposes the level made by a 

 dorsoventral line drawn from the bottom of the sternum (costal 

 angle) to the spinal column. This authorf has devised a simple 

 apparatus for determining the pressure in the small veins of the 

 skin by placing over the vein a small chamber in which the air 

 pressure is raised until the vein disappears. A convenient modi- 

 fication of this apparatus devised by Hooker | is pictured and 

 described in Fig. 206. A small glass capsule is fastened to the 

 skin over a vein by means of a film of collodion solution. The 

 interior of the chamber is connected by rubber tubing with a 

 pressure-bulb and a water manometer. By means of the pressure- 

 bulb the air pressure in the capsule is raised until the vein is just 

 obhterated. The pressure necessary for this result is indicated by 

 the water manometer in centimeters of water, and this is taken to 

 indicate the pressure within the vein. 



With instruments of this kind the degree of pressure neces- 

 sary to obliterate a given vein in the arm, hand, or foot can 

 be determined readily in terms of a column of water, but it is 

 obvious that for any given vein this pressure will vary with the 

 position of the vein. When the hand hangs pendent at the 



* Gaertner, Muench. mediz. Wochenschrift," 1903, 1904. 



t Von Recklinghausen, "Archiv f. exper. Pathol, u. Pharmakol," 55, 470, 

 1906. 



t Hooker, "American Journal of Physiology," 35, 73, 1914; also Eyster and 

 Hooker, "Johns Hopkins Hospital Bulletin," 274, 1908. 



