556 OF THE CIRCULATION OF BLOOD. 



when sitting, 81, and when lying, 80. When the exceptions (which were more numerous 

 in proportion than in males) were excluded, the averages were, standing, 91, sitting, 84, 

 lying, 79; the difference 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 

 standing 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 tem- 

 porarily 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 respect- 

 ively. 



d. 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. 



e. The diurnal variation of the pulse, however, has been made the subject of observation, 

 by Dr. Guy ;* and, as the results of his inquiries have much interest, although (from having 

 been made only on his own person) they may ultimately require some modification, they 

 will be here stated. ' 1. The pulse of a healthy male in a state of rest, unexcited either by 

 food or exercise, is most frequent in the morning, and gradually diminishes as the day ad- 

 vances. , 2 r The pulse diminishes in frequency more rapidly in the evening, than in the 

 morni&g. .3. The diminution in the frequency of the pulse (after excitement) is more regu- 

 lar and progressive in the evening than in the morning. 4. The effect of food is greater 

 and more lasting in the morning, than in the evening ; and in some instances, the same food, 

 which in the morning produces an effect considerable both in amount and duration, has no 

 effect whatever in the evening." It may be hoped that, ere long, this interesting and im- 

 portant subject will receive further elucidation. 



[/. Dr. Valleix has recently published a series of interesting observations on the fre- 

 quency of the pulse in newly-born infants, and in children aged from seven months to six 

 years. He obtained the following results: 1. At birth the pulse is less frequent than at six 

 months; the number of beats in a minute may be stated with considerable exactness to be 

 between 90 and 100. 2. Increase of temperature, even in the slightest degree, invariably 

 produces a notable acceleration of the pulse. The exact ratio between the degree of eleva- 

 tion of temperature and the increase in the frequency of the pulse, is not yet accurately 

 ascertained. 3. Although the observations of Dr. Valleix show a progressive diurnal diminu- 

 tion in the frequency of the pulse, still, he thinks, it would be premature to conclude that 

 these facts support those of Dr. Guy. Dr. Valleix examined his patients in the morning 

 after they had been eating, and to this fact, he thinks, should be attributed the acceleration 

 of the pulse in the early part of the day, and its subsequent diminution towards evening. 

 4. The slightest muscular effort in children is sufficient to augment considerably the number 

 of pulsations. The same is true of any moral emotion. 5. The influence of sex on the 

 pulse is very marked in young children. The pulse is much more frequent in young girls 

 than in boys of the same age. 6. During sleep there is a decided diminution in the number 

 of beats. 7. Between 7 and 27 months there is no sensible change in the frequency of the 

 pulse. Its mean may be stated at 120 beats in the minute, without distinction of sex. If 

 sex be considered, it would be 121 for males and 128 for females. These numbers express 

 the frequency of the pulse at this age under ordinary circumstances, but if a state of perfect 

 cairn is supposed, the numbers would be 119 for the males, and 124 for females. 8. After 

 some observations, not very numerous, however, the pulse would appear to range a little 

 above 100 till six years of age. 9. The mean number of inspirations in a minute in chil- 

 dren aged from 7 months to two years and a half, is between 30 and 32, and is to number 

 of pulsations : : 1 : 4. M. C.] 



3. Movement of the Blood in the Arteries and Capillaries. 



728. We have next to consider the influence of the Arterial tubes on the 

 flow of Blood through them. This influence is exerted by the middle or 

 tibrous coat, which alone is possessed of contractile properties. We find in 

 this coat, a layer of annular fibres, possessing no small resemblance to that 

 of which the muscular coat of the alimentary canal is composed. On the out- 



* Op. cit., vol. iv. p. 69. 



