HEART AND BLOOD. 43 



by the minute orifices mentioned." And shortly afterwards, in 

 the very next chapter, he says : " The more the thorax contracts, 

 the more it strives to force out the blood, the more exactly do these 

 membranes (viz., the sigmoid valves) close up the mouth of the 

 vessel, and suffer nothing to regurgitate." The same fact he 

 has also alluded to in a preceding part of the tenth chapter : 

 " Were there no valves, a three-fold inconvenience would result, 

 so that the blood would then perform this lengthened course in 

 vain ; it would flow inwards during the diastoles of the lungs, 

 and fill all their arteries ; but in the systoles, in the manner of 

 the tide, it would ever and anon, like the Euripus, flow back- 

 wards and forwards by the same way, with a reciprocating 

 motion, which would nowise suit the blood. This, however, 

 may seem a matter of little moment ; but if it meantime appear 

 that the function of respiration suffer, then I think it would be 

 looked upon as no trifle, &c." And again, and shortly after- 

 wards : " And then a third inconvenience, by no means to be 

 thought lightly of, would follow, were the blood moved back- 

 wards during the expirations, had not our Maker instituted 

 those supplementary membranes [the sigmoid valves] ." Whence, 

 in the eleventh chapter, he concludes : " That they have all a 

 common use, (to wit, the valves,) and that it is to prevent 

 regurgitation or backward motion; each, however, having a 

 proper function, the one set drawing matters from the heart, 

 and preventing their return, the other drawing matters into 

 the heart, and preventing their escape from it. For nature 

 never intended to distress the heart with needless labour, nei- 

 ther to bring aught into the organ which it had been better 

 to have kept away, nor to take from it again aught which 

 it was requisite should be brought. Since, then, there are four 

 orifices in all, tAvo in either ventricle, one of these induces, the 

 other educes." And again he says : " Farther, since there is 

 one vessel, consisting of a simple tunic, implanted in the heart, 

 and another, having a double tunic, extending from it, (Galen 

 is here speaking of the right side of the heart, but I extend his 

 observations to the left side also,) a kind of reservoir had to be 

 provided, to which both belonging, the blood should be drawn 

 in by the one, and sent out by the other." 



This argument Galen adduces for the transit of the blood by 

 the right ventricle from the vena cava into the lungs ; but we 



