482 OF THE CIRCULATION OF THE BLOOD. 



l-13th of the whole ; and the difference between standing and lying was 15 beats, 

 or l-5th of the whole. In 50 healthy Females, of the same mean age, the 

 average pulse when standing was 89, when sitting 81, and when lying 80 ; and 

 when the exceptions (which were more numerous in proportion than in males) 

 were excluded, the averages were, standing 91, sitting 84, lying 79 ; the differ- 

 ence between standing and sitting was thus 7 beats, or l-13th of the whole : that 

 between sitting and lying was 4, or l-21st of the whole ; and that between stand- 

 ing and lying was 11, or l-8th of the whole. In both sexes, the effect produced 

 by change of posture increases with the usual frequency of the pulse ; whilst the 

 exceptions to the general rule are more numerous, as the pulse is less frequent. 

 The variation is temporarily increased by the muscular effort, involved in the 

 absolute change of the posture ; and it is only by the use of a revolving board, 

 by which the position of the body can be altered, without any exertion on the 

 part of the subject of the observation, that correct results can be obtained. That 

 the difference between standing and sitting should be greater than that between 

 sitting and lying, is just what we should expect ; when we compare the amount 

 of muscular effort required in the maintenance of the two former positions re- 

 spectively. 



e. The pulse is well known to be much accelerated by Mental excitement, 

 especially by that of the Emotions ; it is also quicker during Digestion ; but on 

 neither of these points can any exact numerical statement be given. 



f. The diurnal variation of the Pulse has been made the subject of observation 

 by Dr. Knox 1 and Dr. Guy ; 3 whose inquiries concur to disprove the usual notion 

 that the pulse rises towards evening, and make it appear that the more common 

 fact is the reverse. It should not be laid down as a general rule, however, that 

 the pulse is most frequent in the morning, unless it be also stated that the exceptions 

 are very numerous. For, whilst out of sixteen healthy, young persons of both 

 sexes examined by Dr. Guy, the pulse was more frequent in the morning in ten 

 individuals by from 2 to 18 beats per minute, it was more frequent in the evening 

 in four individuals by from 9 to 13 beats, and in two others there was no differ- 

 ence. Both these experimenters have remarked, moreover, that the pulse is less 

 excitable, as well as less frequent, in the evening than in the morning ; thus, it 

 was found by Dr. Guy that the very same food which in the morning increased 

 the frequency of the pulse from 5 to 12 beats, and kept it raised above its natural 

 number for one or two hours, produced no effect whatever in the evening ; and 

 it is a matter of ordinary experience that alcoholic liquors have a much more 

 potent effect upon the circulation in the earlier than in the latter part of the 

 day. 



3. Movement of the Blood in the Arteries. 



512. The Blood propelled from the Heart is distributed to the body in general 

 by a system of Arteries, which may be likened in its arrangement to the trunk 

 and branches of a tree, except that very frequent communications or anasto- 

 moses exist among these branches, so that, by continual subdivision and inoscu- 

 lation, their distribution comes more and more to resemble the capillary network 

 in which they terminate (Fig. 141). Although the diameters of the branches, 

 at each subdivision, together exceed that of the trunk, yet there is but little 

 difference in their respective areas. What difference does exist, however, is 

 usually in favor of the branches ; and thus it happens that there is a gradual 

 increase in the capacity of the arterial system from its centre towards the capil- 

 laries, whose capacity is many times greater ( 529). The Arteries exert a 



1 "Edinb. Med. and Surg. Journ.," vol. xi. p. 53. 



2 " Guy's Hosp. Rep.," vol. iv. p. 6( 



