THE CIRCULATION 167 



addicted to drinking brandy ; in them the condition is a con- 

 gestion of the capillary circulation, and is permanent, the ves- 

 sels having lost their power of elastic contraction. 



42. Rapidity of the Circulation. That the blood moves with 

 great rapidity is evident from the almost instant effects of cer- 

 tain poisons, as prussic acid, which act through the blood. 

 Experiments upon the horse, dog, and other inferior animals, 

 have been made to measure its velocity. If a substance which 



expansion will be felt. Now into the rubber tube insert the glass tube, 

 which should be about two feet long and be drawn out to a fine point. 

 Compressing again the bulb of the syringe, the water will be seen to issue 

 from the glass point in a continuous stream, and not in an interrupted 

 one, as from the rubber end. 



The explanation of this is as follows : During each compression of the 

 bulb, the water expands the rubber tubing because its outflow is con- 

 siderably lessened by the resistance of the unyielding glass tube and its 

 much-narrowed end, and during the interval of two compressions, during 

 which the bulb fills again, the rubber tubing contracts upon its contents 

 and slowly expels it. If now the compressions of the bulb are so timed 

 that the rubber tubing is kept stretched, the flow from the glass-end will 

 be continuous. The finger on the tubing will now feel each stroke of the 

 syringe in the decided expansion of the rubber. 



Applied to the circulation of the blood, this experiment shows the 

 following : 



The power of the hand together with the bulb of the syringe represent 

 the heart, which, with each contraction, sends its contents forth into the 

 arteries. These are well represented by the elastic tubing, as they, in 

 reality, are nothing more than that. During the systole of the heart 

 (the compression of the bulb), they are distended to their full capacity ; 

 during the diastole of the heart (represented by the passive filling of the 

 bulb), they contract upon their contents and send it forward toward the 

 capillaries and veins. The latter are represented by the glass tubing, 

 from which we have seen the water issue in a continuous stream. In the 

 capillaries and veins the blood flows in a continuous stream, due to the 

 fact that the force of the heart's action is gradually lost in expanding 

 the arteries, and is felt less and less the farther they are removed from 

 the heart ; the arteries becoming smaller and smaller, the intermittency 

 of the flow is lost when the capillaries are reached. 



The expansion which the finger feels when placed upon the rubber 

 tubing represents the pulse, which is the maximum distension of the 

 artery at that point. 



42. Show what time is required for a given portion of blood to travel once around the 

 body. 



