CAPILLARY BLOOD-PRESSURE OF MAN 273 



demonstrated in the laboratory by direct observation on the web of the 

 frog's foot by the use of the compound microscope. Give a 4o-gm. frog a 

 hypodermic injection of 0.3 c.c. of ether under the skin of the back. Wet 

 a piece of cheesecloth the size of a handkerchief with tap water and wrap 

 the etherized frog so as to cover the entire body with the exception of the 

 foot. When the anesthesia has progressed so as to destroy voluntary 

 movements, bind the foot on an ordinary frog board and spread the web 

 over the window in the board. Choose an area of the skin which shows 

 small arteries, capillaries, and veins, and in which the blood is flowing 

 freely and rapidly. Examine with the low-power of a compound micro- 

 scope. In a favorable field small arteries, capillaries, and veins with 

 blood flowing rapidly through them will be easily found. Choose one 

 such field, cover with a piece of thin cover-glass, moisten with a drop 

 of water if necessary, and examine with a high power. Note in the small 

 artery the pulsating current; the border of clear fluid along the side of the 

 main stream of blood; the white corpuscles along the clear borders of the 

 current. In the small veins there are usually no pulsations and the speed 

 of the current is somewhat less. Careful examination of the capillaries 

 will reveal a delicate wall, the individual corpuscles, and the fact that the 

 red corpuscles are actually larger than the diameter of the capillary at 

 some points and must be bent to pass through. Note that the capillaries 

 form an intricate and anastomosing network; that the current may occa- 

 sionally be reversed in some of the anastomoses. 



The anesthetizing effect of the ether recommended will usually con- 

 tinue about 10 to 20 minutes. If the observation is more prolonged, a 

 second dose of ether should be given. The capillaries in the tails of small 

 fish are often very readily observed, and these may be substituted for the 

 frog's web. 



20. Capillary Blood-Pressure of Man. Measure the capillary blood- 

 pressure in your own finger by von Krie's method. This apparatus con- 

 sists of a small piece of glass an inch square, or less, which is placed across 

 the knuckle of the finger just back of the nail. A small weight pan is 

 suspended by a loop of thread over this glass plate so that weights put in 

 the pan will bring varying pressure on the plate above. Add weights to the 

 pan until an area of the skin, about 5 mm. in diameter, is blanched by the 

 pressure. Mark the outline of this bloodless area on the glass, take 

 off the apparatus and measure the exact area of the glass so marked, weigh 

 the entire apparatus and compute the pressure in grams per square centi- 

 meter for the area. This pressure in terms of mercury represents the 

 capillary blood-pressure in the vessels of the skin of the finger at that 

 level. Measure the pressure when the finger is held at the level of the top 

 of the head; with the finger held as low as possible; held at the level of the 

 heart. Tabulate the measurements. The capillary blood-pressure at the 

 level of the heart is usually from 40 to 50 mm. of mercury. 



