184 THE BLOOD. 



lation cither does not take place, or is accomplished in so im- 

 perfect a manner, that the clot is scarcely recognizable as 

 such. 



6. The following is a modification of an experiment of 

 Briicke, devised by my friend Dr. Durante. In a rabbit, two 

 small incisions are made across the course of the external jugu- 

 lar vein, (see 48) one near the clavicle, the other near the 

 origin of the vessel great care being taken not to go deeper 

 than is necessary in order to see the vessel through the fascia. 

 A small needle is then passed under the vein near the proxi- 

 mal incision, in a direction at right angles to that of its axis, 

 and corresponding to that of the incision, but deeper. A 

 second needle is then laid in the course of the incision, and 

 drawn tightly towards the first by a ligature at either end, by 

 which means the blood current is entirely arrested, while the 

 coats of the vein are absolutely protected from injury. A 

 second pair of needles is then inserted at the distal incision, 

 and secured in a similar manner, so as to shut in the blood 

 with which the vein becomes distended after the tightening of 

 the first ligature. After the lapse of a couple of days, the 

 ligatured portion of the vein is exposed at some part of its 

 course, and punctured with a glass pipette, by means of which 

 the blood is withdrawn from it by suction in a perfectly liquid 

 state. On removing the needles the natural circulation is at 

 once restored. This result, however, is only obtained when the 

 greatest care is used to avoid injury to the coats of the vein. 

 This may be readily proved by repeating the experiment 

 (which, in a practical point of view, is of great importance) in 

 a different way. If, instead of using needles, ordinary liga- 

 tures are placed on the points indicated, a coagulum is formed, 

 so that on pinching the vein no blood flows. On opening such 

 a vessel it is found to be occupied by two clots (thrombi), each 

 of which is thickest and firmest at the ligature, and becomes 

 thinner and looser towards the middle of the deligated part. 

 Dr. Durante has shown that, in this experiment, this absence of 

 coagulation depends on the integrity of the endothelium. 

 Wherever the endothelium of a vein is irritated so as to 

 undergo germination, a clot is formed which is co-extensive 

 with the alteration of the endothelial elements. 



1. The arterial trunks leading from the heart of a frog or 

 tortoise are first tied, and then (as soon as the heart has be- 

 come distended) the venous trunks. The heart full of blood 

 is removed from the body and suspended in a small flask by 

 one of the ligatures. The flask is allowed to stand so long as 

 the heart continues to pulsate. If, then, before the pulsations 

 have entirely ceased, the blood is allowed to flow from the 

 heart by removing the arterial ligatures, it is seen to be fluid. 



