506 CIRCULATION OF BLOOD AND LYMPH. 



factor is always the psychical element. The mental interest 

 that the individual experimented upon takes in the procedure 

 almost always causes a rise of pressure and perhaps a changed 

 heart rate. Results, as a rule, upon any individual show lower 

 values after the novelty of the procedure has worn off, and the 

 patient submits to the process as an uninteresting routine. Under 

 normal conditions, Potain* estimated the systolic pressure in the 

 radial of the adult at about 170 mms. of mercury and the varia- 

 tions for different ages he expressed in the following figures: 



Age 6-10 15 20 25 30 40 50 60 80 



Pressure (systolic). 89 135 150 170 180 190 200 210 220 



Without the other side of the picture that is, the diastolic pres- 

 sure and the force of the heart beat (pulse pressure) it is difficult 

 to interpret these figures. The rapid increase up to maturity 

 probably represents chiefly the larger output of blood from the heart ; 

 the slower and more regular increase from maturity to old age is 

 due possibly to the gradual hardening of the arteries, since the less 

 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.f 



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 



! "La pression arterielle de I'homme," Paris, 1902. 



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

 1904. 



