288 CIRCULATION. 



for a length of time. A corpuscle is frequently seen caught 

 at the angle where a vessel divides into two, remaining fixed 

 for a time, distorted and bent by the force of the current. 

 It soon becomes released, and, as it enters the vessel, regains 

 its original form. In some of the vessels of smallest size, the 

 corpuscles are slightly deformed as they pass through. 



The scene is changed with every different part which is 

 examined. In the tongue, in addition to the arterioles and 

 venules, with the rich network of capillaries, dark-bordered 

 nerve-fibres, striated muscular fibres, and pavement epithe- 

 lium can be distinguished. In the lungs, the view is very 

 beautiful. Large, polygonal air-cells are observed, bounded 

 by capillary vessels, in which the corpuscles move with ex- 

 treme rapidity. It has been observed that the larger vessels 

 are crowded to their utmost capacity with corpuscles, leaving 

 no still layer next the walls, such as is seen in the circulation 

 in other situations. 



When the circulation has been for a long time under 

 observation, as the animal becomes enfeebled, very interest- 

 ing changes in the character of the flow of blood take place. 

 The continuous stream in the smallest vessels diminishes 

 in -rapidity, and after a while, when the contractions of the 

 heart have become infrequent and feeble, the blood is nearly 

 arrested, even in the smallest capillaries, during the intervals 

 of the heart's action, and the current becomes remittent. 

 As the central organ becomes more and more enfeebled, the 

 circulation becomes intermittent ; the blood receiving an 

 impulse from each contraction, but remaining stationary 

 during the intervals. At this time, the corpuscles cease to 

 occupy exclusively the central portion of the vessels, and the 

 clear layer of plasma next their walls, which was ob- 

 served in the normal circulation, is no longer apparent. 

 Following this, there is actual oscillation in the capillaries. 

 At each contraction of the heart, the blood is forced onwards 

 a little distance, but almost immediately returns to about its 

 former position. This phenomenon has long been observed, 



