4 Professor T. Clifford Allhvtt [Feb. 3, 



whereas the air-bag turns the intermittent blowing into a continuous 

 feed of air. In the arterial system of man the same provision is made ; 

 its tubing is highly elastic, and a chief part of it — namely, the aorta 

 — being relatively wider than other branches of the tree, contains, 

 hke the bagpipe reservoir, accommodation for very variable supplies- 

 of output from the heart pump. Thus a very large part of the heart 

 power is used in dilatation of the vessels, and by these is given back 

 to the blood. The valves of the heart serve a like purpose of 

 regulating the pressure of the supply to the vascular system. 



The lecturer in the next place dealt with the pulse, contrasting 

 the travel of the wave with the travel of the blood itself. The wave 

 due to the shock of the heart beat travels, ordinarily, about twenty 

 times as fast as a given particle of the blood itself. The tenser the 

 walls of the arteries the faster the wave travels along the taut vessels, 

 but the slower the passage of the blood itself. Herein hes one of the 

 chief evils of a morbid rise of arterial pressure ; more stress on the 

 vessels, less distribution of their contents. Many of these processes 

 were illustrated by lantern slides and demonstrations by Dr. Dixon, 

 demonstrator of pharmacology in Cambridge. 



After these principles Dr. Dixon exhibited the various instruments 

 in use for measuring blood pressures in man, and the means by which 

 their curves may be recorded on a revolving drum (kymograph). 



The lecturer then entered upon the vital properties of the arteries 

 —that they are not only elastic, and so accommodate themselves to 

 the varying pressures, but are endowed also with nervous governance, 

 whereby they effect a large economy in work and material. Several 

 functions of the human body cannot, save within small hmits, work 

 together. If we are digesting, we are not apt for thought ; the 

 Alpine cUmber is mercifully unable to worry over affairs — his mind is. 

 put into abeyance, and so on. Thus the arterial system by the means 

 of its nervous connections, contracting in some areas and dilating in 

 others, automatically diverts its f ertihsing streams hither or thither as 

 needs arise. Moreover, it can enlarge or diminish its bed according to 

 the total quantities of blood temporarily in active circulation — a quan- 

 tity which is very variable. By contracting the arteries in considerable 

 areas and correspondingly dilating them in others, the fields of the 

 various functions of the body can be used alternately, as we see in the 

 irrigation of Alpine meadows. By the same means the very various 

 pressures of the blood can be counteracted. When under muscular 

 effort, for instance, the pressure is raised, a corresponding area outside 

 the muscles is dilated, and pressure more or less equalised ; thus the 

 heart is enabled to do the most work with the least disturbance of 

 stresses. So in a bath, cold or very hot, the crimping up of the large 

 cutaneous areas is compensated by large dilatations in internal areas, 

 and pressures return to the normal in two or three minutes. The 

 chief area in which blood can be accommodated, and thus for a time 

 put out of circulation, is a large abdominal area. 



