188 THE MOTION OF THE BLOOD. 



The elastic coat both assists and antagonises the muscular : 

 assists it in preventing distension when the distending force is 

 very strong, and antagonises it tends to prevent the canal from 

 becoming too narrow when it attempts to contract the vessel 

 excessively. <i 



Still, independently of the whole quantity of blood, and of the 

 heart's action, particular arteries may be in various degrees of 

 distension, according to the various states of their individual 

 contraction. For example, when a finger has a whitlow, the 

 digital branches are found larger than usual at the very roots of 

 the fingers ; in many affections the pulse of the two wrists differ 

 for a time. In fact, their condition may vary like that of the 

 capillaries, and probably does vary every time that altered cir- 

 culation occurs in a part, although Dr. Parry's opinion holds true 

 during the tranquil and ordinary condition of circulation. I am 

 thus inclined to agree with and differ from both Dr. Parry and 

 Dr. Hastings ; believing the former to be right as to the ordinary 

 state, the latter in irregularity. In some diseases the action of 

 the heart is strong and the pulse weak, and vice versa ; so that it is 

 frequently right to examine both. 



The elastic power is said to be greater in the arteries, and the 

 muscular in the capillaries ; and as the muscular power is proved 

 by Dr. Parry's experiments to be able to overcome the elastic in 

 the arteries, it must be very considerable in the capillaries. 



Dr. Curry, a late lecturer on the practice of medicine at Guy's 

 Hospital, concluded, without doubt hypothetically, from some 

 microscopic experiments which he had made on inflammation in 

 the presence, once of Sir Charles Bell and once of Mr. Travers, 

 that the circulation is indispensably facilitated by a sort of electric 

 repulsion between the vessels and their contents, and that in in- 

 flammatory accumulation, the tone of the vessels being impaired, 

 this repulsion is diminished, and the blood passes onwards with 

 difficulty in consequence. 1 ' 



" Since Whytt s , especially, and other illustrious physiologists 



q On the operation of the elastic and muscular coats, see J. Hunter, 1. c. 

 p. 118. sqq. 



r See the Syllabus of his lectures for 1810. 



" Consult his Physiological Essays, containing an inquiry into the causes which 

 promote the circulation of the fluids in the very small vessels of animals. Second 

 edition, Edinb. 1761. 12mo. 



H. v. d. Bosch, iiber das Muskelvermogen der ffaargefdssgen. Munster, 1 786. 

 8vo." 



