BLOOD PRESSURE IN A MAMMAL AND ITS REGULATION 261 



found. Choose one such field, cover with a piece of thin cover-glass, moisten- 

 ing 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 slight pulsations; and the white cor- 

 puscles that will be found flowing along the borders of the current. In the 

 small veins there are usually no pulsations and the speed of the current is 

 somewhat less. In the capillaries a careful examination will reveal a deli- 

 cate 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 occasionally reverse itself in 

 some of the anastomoses. 



The anesthetizing effect of the dose of ether recommended will usually 

 continue about 15 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. 



1 8. Capillary Blood Pressure. Measure the capillary blood pres- 

 sure in your own finger by von Krie's method. This apparatus consists 

 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 glass so marked, weigh the entire apparatus 

 and compute the pressure per square centimeter for the area. This pres- 

 sure in terms of mercury represents the capillary blood pressure in the vessels 

 of the skin of the finger at that level. Vary the experiment by measuring 

 the pressure with the finger 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. 



19. The Arterial Blood Pressure in a Mammal and Its Nervous 

 Regulation. After the student has measured the arterial blood pres- 

 sure by Hale's method, described above, he is in a position to study the 

 variations and co-ordinations in the blood circulatory apparatus. The re- 

 cording apparatus consists of writing pens, seconds time marker, signal 

 marker, blood- pressure manometer preferably Ludwig's mercury manom- 

 eter, and a continuous paper kymograph preferably Ludwig's weight- 

 driven form for a continuous record of the arterial blood pressure. Connect 

 the cannula with the mercury manometer which is provided with a pressure 

 bottle. Use a cannula of the form shown in figure 185, connecting the side 



