CONSTRUCTION OF ARTERIES AND VEINa 41 



it with tremendous velocity : it then acquires inflammation, and becomes ul 

 cerated (see sect. 391; a disposition which must be increased whenever the 

 blood has been formed imperfectly, either as regards the lungs or the lacteala 

 So much is this the case, that the blood drawn from a very aged patient of 

 mine lately, that was iucapable of grinding his corn properly, showed evident 

 proofs that particles of ill-digested food had entered into the circulation, and 

 is an answer to those writers who aver that the lacteals reject the bile and 

 suck up only the fine parts of the chyle ; whereas, all inquiring persons must 

 know, that they take up the lighter parts of all substances whatever that pass 

 through the intestines. 1( this were not so, how is it that the slow poisons 

 just spoken of enter the blood 7 or how would it come to pass that so much 

 good is performed by alterative medicines, that, m like manner, insensibly in- 

 troduce themselves into the blood, and produce invisibly those permanently good 

 effects we so much admire 7 The opposition of a few is no obstacle to this 

 commendation of an obscure but safe and certain class of medicines, — to say 

 nothing of an alterative regimen, which is mtre safe still, and certainly more 

 natural, though slower and less positive in its effects than active medicine. 

 How much longer is the horse to be treated with nothing else but violence 7 



42. Blood-vessels, or tubes, I have already observed, pervade every part 

 of the body, and are of two kinds, whose office is directly the reverse of each 

 other. Arteries, it will be recollected, convey the vital fluid to all parts of the 

 body, and the construction of these, it may easily be conceived, from what has 

 been said, is simply that of a tube with great contractile powers : they are 

 large near the heart, but soon branch out of a lesser size, until, entering the 

 smaller organization of the solids, they become very minute, infinitely nume- 

 rous, and more sensitive, thus affording the means of renovation, or growing 

 to the flesh, bones, skin, hair, hoofs, &c. The large artery communicates with 

 minor branches, soon after leaving the heart, by two rows of openings, like 

 perforations, in its lower sides, at two or three inches asunder. Some one has 

 likened the arrangement of these vessels to the stem, branches, and twigs of 

 a currant-bush, and so might the veins that run nearly parallel to the ar- 

 teries, through every part of the animal, but are so constructed and arranged, 

 as to take up and reconvey the blood (which the arteries constantly deposit) 

 back again to the heart; and the similarity will still further hold good, if wo 

 extend it to the leaves of the bush, and compare these to the glands (see Sec- 

 tians 27, 28), in every one of which an artery terminates, and deposits its nu- 

 tritious contents, and where every small vein begins the absorption of what 

 the artery has so left behind. This absorption, when obstructed, lax, or other- 

 wise imperfect on the surface, may be restored by stimulating the parts with 

 spirits ; when it is too high, and labouring greatly in consequence of the vis- 

 cidity of the blood, local inflammation is engendered, and one or other of those 

 diseases I shall hereafter treat under " abscess," is the consequence of this 

 constitutional derangement. Blood that is thick, heavy, or viscid — call it 

 which we like — causes heat, which being general, is fever ; the rapidity of the 

 circulation increases violently, and the blood becomes more fluid than when 

 the animal was in good health. Arteries may be distinguished from veins 

 in the dead subject, by the property they possess, of retaining their tubulai 

 shape after the blood is discharged ; whereas, the veins collapse, when empty. 



43, If the arteries are plain tubes, lying for the most part concealed, the 

 veins, on the contrary, are more frequently found exposed to the sight under 

 the skin, next to the muscle. But, more delicate and more numerous, the 

 veins perform their part of the circulation by a totally different means than i* 

 found in the })ropulsion and contraction of the arteries. One of the means 

 of effecting this purpose is by the obvious and simple movement of the bcxly 

 and limbs, as well as by the act of breathing, whereby the blood is presieJ sy^ii 



