O H. VV A 1. XI V S 



PECQUET'S FIGURE OF THE THORACIC DUCT IN THE DOG. 



FIGVR EXPLICATIO. 



EXPERIMENT OF WALRUS ON THE FLOW OF 

 BLOOD IN THE FEMORAL VEIN. 



The ligature " CD placed under the artery 

 and vein which fast binds tlie thigh is shown 

 in the right leg, lest the confusion of the 

 lines might disturb the spectator in the left 

 thigh." 



Harvey's work, supplemented with the discovery of the capillaries 

 and that of the lymphatic system, marks a new era in physiology. It 

 revolutionized the whole subject, for now the examination of the 

 exchanges between the blood of the organs and tissues of the body 

 became possible. The idea of " spirits " ought to have disappeared, 

 but it did not. The very title of his work suggests the wide view 

 Harvey took of the problem ; Harvey made accurate anatomical 

 observations and planned experiments to test his hypotheses, and he 

 made abundant use of his knowledge of comparative anatomy, and 

 with convincing results. 



" If a live snake be laid open, the heart will be seen pulsating quietly, distinctly, for 

 more than an hour, moving like a worm, contracting in its longitudinal dimensions, (for 

 it is of oblong shape,) and propelling its contents ; becoming a paler colour in the systole, 

 of a deeper tint in the diastole ; and almost all things else by which I have already said 

 that the truth I contend for is established, only that here everything takes place more 

 slowly, and is more distinct. This point in particular may be observed more clearly than 

 the noonday sun ; the vena cava enters the heart at its lowest part, the artery quits it 

 at its superior part ; the vein being now seized either with forceps or between the finger 

 and thumb, and the course of the blood for some space below the heart interrupted, you 

 will perceive the part that intervenes between the fingers and the heart almost 

 immediately to become empty, the blood being exhausted by the action of the heart ; at 

 the same time the heart will become of a much paler colour, even in its state of dilatation, 

 than it was before ; it is also smaller than at first, from wanting blood ; and then it begins 

 to beat more slowly, so that it seems at length as if it were about to die. But the impedi- 

 ment to the flow of blood being removed, instantly the size and colour of the heart are 

 E 



