PHENOMENA OF THE CAPILLARY CIRCULATION. 285 



distributes itself by the capillaries ; and finally, having per- 

 formed its office, how it is collected and carried off by the 

 veins. 1 



In studying the circulation under the microscope, the an- 

 atomical division of the blood into corpuscles and a clear 

 p]asma is observed. This is peculiarly evident in cold-blood- 

 ed animals, the corpuscles being comparatively large, and 

 floating in a plasma which forms a distinct layer next the 

 walls of the vessel. The white corpuscles, which are much 

 fewer than the red, are generally found in the layer of 

 plasma. 



In vessels of considerable size, as well as the capillaries, 

 the corpuscles, occupying the central portion, move with 

 much greater rapidity than the rest of the blood, leaving a 

 layer of clear plasma at the sides, which is nearly immovable. 

 This curious phenomenon is in obedience to a physical law 

 regulating the passage of liquids through capillary tubes for 

 which they have an attraction, such as exists, for example, 

 between the blood and the vessels. In tubes reduced to a 

 diameter approximating to that of the capillaries, the attractive 

 force exerted by their walls upon a liquid, causing it to enter 



1 Various methods of preparing the animal for examination have been em- 

 ployed. The one we have found most convenient, in examining the circulation 

 in the frog, is to break up the medulla with a needle, an operation which does not 

 interfere with the circulation, and attach the animal by pins to a thin piece of 

 cork, stretching the web over an orifice in the cork, to allow the passage of light, 

 and securing it with pins through the toes. The membrane is then moistened with 

 water, and covered with thin glass, and if the general surface be kept moist, the 

 circulation may be studied for hours. (See " Phenomena of the Capillary Circula- 

 tion," an inaugural thesis, by the author, American Journal of the Medical Sciences, 

 July, 1857.) By gently inflating the lungs with a small blow-pipe, securing them 

 by a ligature passed around the larynx beneath the mucous membrane, and open- 

 ing the chest, the circulation may be examined in this situation. It may be stu- 

 died in the tongue (which presents a magnificent view of the circulation as well as 

 the nerves and muscular fibres) by drawing it out of the mouth, and spreading it 

 into a thin sheet, securing it with pins. The circulation may be studied in the 

 mesentery of a small warm-blooded animal, like the mouse, by fixing it upon the 

 frog-plate, opening the abdomen, and drawing out the membrane; but not as 

 well or as conveniently as in the tongue or web of the frog. 



