VELOCITY AND PRESSURE OF BLOOD-FLOW. 509 



elastic the arteries become, the greater will be the systolic rise with 

 each heart beat. Owing to the method Potain used these figures 

 are all undoubtedly too high, but the relative values are probably 

 correct. With his more complete apparatus Erlanger reports 

 that in the adult (20 to 25), when the psychical factor is ex- 

 cluded, the average pressure in the brachial is 110 mms., systolic, 

 and 65 mms., diastolic, figures much lower than those given by 

 Potain. Von Recklinghausen's figures for the same artery are, 

 systolic pressure 116 mms. Hg, diastolic pressure 73 mms. Hg. 



Erlanger and Hooker report observations upon the effect 

 of meals, of baths, of posture, the diurnal rhythm, etc.* 



The effect of meals is particularly instructive in that it illustrates 

 admirably the play of the compensatory mechanisms of the circu- 

 lation by means of which the heart and the blood-vessels are ad- 

 justed to each other's activity. During a meal there is a dilatation 

 of the blood-vessels in the abdominal area, or, as it is frequently 

 called in physiology, the splanchnic area, since it receives its 

 vasomotor fibers through the splanchnic nerve. The natural 

 effect of this dilatation, if the other factors of the circulation 

 remained constant, would be a fall of pressure in the aorta and a 

 diminution in blood-flow to other organs, such as the skin and the 

 brain. This tendency seems to be compensated, however, by an 

 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.f It consists simply in raising 

 slowly the 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 



* Erlanger and Hooker, "The Johns Hopkins Hospital Report," vol. xii, 

 1904. 



t Muench. mediz. Wochenschrift," 1903, 1904. 



