CIRCULATION OF THE BLOOD 101 



CHAPTER VII 



THE BLOOD PASSES THROUGH THE SUBSTANCE OF THE LUNGS 

 FROM THE RIGHT VENTRICLE OF THE HEART INTO THE 

 PULMONARY VEINS AND LEFT VENTRICLE 



THAT this is possible, and that there is nothing to prevent 

 it from being so, appears when we reflect on the way in 

 which water permeating the earth produces springs and 

 rivulets, or when we speculate on the means by which the 

 sweat passes through the skin, or the urine through the 

 substance of the kidneys. It is well known that persons 

 who use the Spa waters or those of La Madonna, in the ter- 

 ritories of Padua, or others of an acidulous or vitriolated 

 nature, or who simply swallow drinks by the gallon, pass 

 all off again within an hour or two by the bladder. Such a 

 quantity of liquid must take some short time in the con- 

 coction: it must pass through the liver (it is allowed by all 

 that the juices of the food we consume pass twice through 

 this organ in the course of the day) ; it must flow through 

 the veins, through the tissues of the kidneys, and through 

 the ureters into the bladder. 



To those, therefore, whom I hear denying that the blood, 

 aye, the whole mass of the blood, may pass through the 

 substance of the lungs, even as the nutritive juices percolate 

 the liver, asserting such a proposition to be impossible, and 

 by no means to be entertained as credible, I reply, with the 

 poet, that they are of that race of men who, when they 

 will, assent full readily, and when they will not, by no 

 manner of means; who, when their assent is wanted, fear, 

 and when it is not, fear not to give it. 



The substance of the liver is extremely dense, so is that 

 of the kidney; the lungs, however, are of a much looser 

 texture, and if compared with the kidneys are absolutely 

 spongy. In the liver there is no forcing, no impelling 

 power; in the lungs the blood is forced on by the pulse of 

 the right ventricle, the necessary effect of whose impulse is 

 the distension of the vessels and the pores of the lungs. 

 And then the lungs, in respiration, are perpetually rising 

 and falling: motions, the effect of which must needs be 



