168 PHYSIOLOGY CHAP. 



The office of the heart in its movements is to drive the blood 

 from the veins to the arteries, and distribute it throughout the 

 body. Since the ventricular septum is impermeable, the whole of 

 the blood must, as recognised by Columbus, traverse the lungs by 

 the arterial vein and the venous artery, in order to pass from the 

 right to the left ventricle. None of this is fundamentally new ; 

 it is only the correction of certain fallacies of Galen in regard to 

 the movements of the heart. 



The concept of the general circulation is expressed clearly by 

 Harvey in the following words : " Patet sanguinem in quodcumque 

 membrum per arterias ingredi, et per venas reineare : et arterias 

 vasa esse deferentia sanguinem a corde, et venas vasa et vias esse 

 regrediendi sanguinis ad cor ipsum ; et in rnernbris et extremitatibus 

 sanguinem (vel per anastornosin immediate, vel mediate per carnis 

 porositates, vel utroquoque modo) transire ab arteriis in venas ; 

 sicut ante in corde et thorace a venis in arterias ; unde in circuitum 

 moveri, illinc hue et hinc illuc, e centre in extrema scilicet, et ab 

 extremis rursus ad centrum, nianifestum fit." 



To establish his theories he gives experimental evidence of the 

 three following propositions : 



1. The blood expelled by the contractions of the heart passes 

 incessantly from the vena cava to the arteries in such quantity 

 " ut ab assumptis suppeditari non possit, et adeo ut tota rnassa 

 brevi tempore illinc pertranseat." 



2. The blood driven forward by the arterial pulses penetrates 

 continuously to every member or part of the body, " majori copia 

 multo, quam nutritioni necessarium sit, vel tota massa suppeditari 

 possit." 



3. "Ab uno quoque membro, ipsas venas hunc sanguinem 

 perpetuo retroducere ad cordis locum/' 



The experimental proof of the first proposition is the most 



original part of Harvey's work. Starting from the capacity of the 



right ventricle in man (which contains a little over 3 oz. of blood) 



\ he pointed out that a considerable quantity of blood must be 



\ driven into the arteries at each systole, owing to the width of the 



orifices and the force of contraction. Whatever this quantity, it 



I must be in relation with the difference in the capacity of the con- 



} tracted and the dilated ventricle. If the heart of man or other 



animals expels only one dram of blood in one contraction, and if it 



contracts a thousand times in half an hour, then in this short time 



it must drive ten pounds and five ounces of blood into the arteries, 



a quantity far too large to be derived from the nutritive elements 



taken into the system, unless the blood returns by the same path. 



On opening, not the aorta, but any small artery, the whole of the 



> blood in the body escapes in less than half an hour, as was noted 



Vby Galen. 



The evidence for the second statement is merely an extension 



