124 CIRCULATION OF THE BLOOD. 



stitution of the blood, the rigidity or laxity of the tissues, and 

 the like. A thicker blood, of course, moves more slowly 

 through narrower channels ; it is more effectually strained in 

 its passage through the substance of the liver than through 

 that of the lungs. It has not the same velocity through flesh 

 and the softer parenchymatous structures and through sinewy 

 parts of greater compactness and consistency : for the thin- 

 ner and purer and more spirituous part permeates more 

 quickly, the thicker more earthy and indifferently concocted 

 portion moves more slowly, or is refused admission. The 

 nutritive portion, or ultimate aliment of the tissues, the dew or 

 cambium, is of a more penetrating nature, inasmuch as it has 

 to be added everywhere, and to everything that grows and is 

 nourished in its length and thickness, even to the horns, nails, 

 hair and feathers ; and then the excrementitious matters have 

 to be secreted in some places, where they accumulate, and either 

 prove a burthen or are concocted. But I do not imagine that the 

 excrementitious fluids or bad humours when once separated, nor 

 the milk, the phlegm, and the spermatic fluid, nor the ultimate 

 nutritive part, the dew or cambium, necessarily circulate with 

 the blood : that which nourishes every part adheres and be- 

 comes agglutinated to it. Upon each of these topics and va- 

 rious others besides, to be discussed and demonstrated in their 

 several places, viz., in the physiology and other parts of the 

 art of medicine, as well as of the consequences, advantages or 

 disadvantages of the circulation of the blood, I do not mean to 

 touch here ; it were fruitless indeed to do so until the circu- 

 lation has been established and conceded as a fact. And here 

 the example of astronomy is by no means to be followed, in 

 which from mere appearances or phenomena that which is in 

 fact, and the reason wherefore it is so, are investigated. But as 

 he who inquires into the cause of an eclipse must be placed 

 beyond the moon if he would ascertain it by sense, and not by 

 reason, still, in reference to things sensible, things that come 

 under the cognizance of the senses, no more certain demon- 

 stration or means of gaining faith can be adduced than exami- 

 nation by the senses, than ocular inspection. 



There is one remarkable experiment which I would have every 

 one try who is anxious for truth, and by which it is clearly shown 

 that the arterial pulse is owing to the impulse of the blood. Let 



