6

LECTURES ON THE

from this caufe. For if thefe phenomenon were owing tothe heart, it would be equally difperfed over the -wholebody. if to refpiration, over the whole fuperior part.Haller endeavours to account for this, from the plexus ofnerves obferVed round the arteries; but in thefecond volumeof his Elemtnta Physiologic, he has confeff:d, that the nerveshave no contraSibiiity,and has given up the quefhan. Thisbeing given up, there feems no method of accounting forthis, bat from extenfioii of nervous power to the arteries;and, indeed, it appears, that fuch a thing takes place inmorbid phaenomena. In the rheumatifm, e. g. it is acommon thing to find the arteries, near the parts affefled,tenfer than any where elfe ; and in a hemiplegia, the pulfeis weak eft on the affefted fide. As to the obje&ion, of themufcular coats being tendinous, Anatomifts allege, thatin the Small arteries there is no mufcular appearance: Butit is probable, that the coat here is only more lax, and thatby analogy we may infer a mufcular aflion in the largerarteries, although they have a tendinous appearance.This opinion is the more probable, as the tendinousparts encreafe over the mufcular fibres by age. The con-traclibility of the excretories of the glands is evinced by fewexcretions, fweat excepted ; being promoted by the increafedaction of the heart , although they are by irritation of theexcretories. Another proof is, that by irritating a part,which has a great fympathy with the gland, the excretion ispromoted: e. g. harfh founds, and grating of the teeth,promote the flow of faliva ; anger, contufions, and fra&ureof the head, evacuation of the bile, &c.

If the fecretory and excretory organs are liable to be thusaffefted, the fluid feereted will, of confequence, be altered,and this alteration is to be imputed to the ftate of thefecerning organ, and not to the nature of the fluid. Forthis reafon the laws of the nervous power ought to beftudied with the utmoft attention. Thefe I fhall treat moreparticularly when I come to treat on fedative and ftimulantmedicines. At prefent I fhall make fome general applicationfrom what has been faid. In the common fyftem great.flrefsis laid on the laxity and rigidity of the fimple folid fibres.Although thefe propertiesarenot altogether to be difregarded,yet there are few inftances of any fudden changes in thefimple fibres, but they feem to increafe uniformly in firtn-nefs, as the perfon is advanced in age; and I have no ideaof any difeafe in old people depending on their laxity. I

believe,