AND BLOOD PRESSURE 135 



energy can be no less than that effected by the heart and vaso- 

 motor system, and is, probably, as important in controlling the 

 flow of blood. In the active conditions of life the contents of 

 the capillaries are continually being emptied onwards by the 

 contractions of the skeletal muscles, pressure against external 

 bodies, and the influence of gravity in changes of posture. The 

 capillary system is as a sponge squeezed and filled continually by 

 the active motions of the body. The attempts which have been 

 made to estimate capillary pressure have all been made on trans- 

 parent membranes in the motionless animal fixed in the horizontal 

 position, or on man's skin with the part fixed, immobile during 

 the observation. In the animal microscopic observations have 

 been made by Roy and Brown on the frog's mesentery, the 

 capillaries being compressed by a sheet of transparent peritoneal 

 membrane which formed the base of a glass capsule, in which the 

 fluid pressure could be made greater or less. A pressure of 100 

 to 250 mm. H 2 sufficed to stop the circulation in the capillaries 

 under these conditions, while a pressure of 200 to 350 mm. H 2 

 expelled the blood from the arterioles. When the heart was in- 

 hibited the pressure sank to 0, rising again to 70 to 100 mm. H 2 

 as the veins filled. The anaemia so produced was followed by 

 hyperaemia and increased pressure. 



Measurements of capillary pressure have been made on man 

 by v. Kries, v. Recklinghausen, and others, the method being the 

 finding of that pressure which just blanches the skin. V. Kries 

 weighted a glass plate 4 sq. mm. big placed behind the finger nail. 

 He found 0'25 grm. was the smallest difference which produced a 

 visible effect. Now as 1 grm. equals the weight of 1 c.c. of H 2 0, 



= :~=250 mm., the error of observation would be 



4 8( mm 

 250 

 4aq~innf = ^ ^ rmn ' ^0, a very large one considering the smallness 



of the pressure measured. H. W. Recklinghausen places a small 

 flaccid rubber bag on the skin, through the centre of which he has 

 punched a hole. He moistens skin and bag with glycerine, and 

 covers the hole with a glass slide, holding it so as to make an air- 

 tight junction between bag skin and glass, and then through a 

 side tube blows air into the bag until the skin blanches. A mano- 

 meter connected with the side tube gives the pressure. These 

 methods necessitating the fixation and immobility of the part, cannot 

 be applied rapidly, and therefore do not give the capillary pressure 



