MOTION OP THE BLOOD IN THE CAPILLARIES. 495 



vessels, so as to produce a great amount of friction and a consequent retardation ; 

 the continual arrival of new corpuscles thus produces an accumulation which 

 completely fills the vessels of the part, and thus occasions a total stagnation ; 

 but this gives place to the renewal of the current, by the dispersion of the cor- 

 puscles, soon after the withdrawal of the stimulus. A very similar set of 

 phenomena has been observed by Mr. Wharton Jones, 1 as the consequence of the 

 direction of a stream of carbonic acid against the capillary network. And the 

 depression of the vitality of the part, by such injuries as tend to excite Inflamma- 

 tion in it, produces a like stagnation. This effect cannot be attributed to me- 

 chanical obstruction in the vessels, for they are usually dilated, rather than 

 contracted, when this condition exists ; and without any change in the dimen- 

 sions of a tube, the stream of blood through it may be seen decreasing from 

 extreme velocity to complete stagnation. 3 That alterations in the chemical 

 state of the blood (involving, of Bourse, important changes in its vital properties) 

 are capable of exercising a most important effect on the Capillary circulation, 

 is shown, not merely by the stagnation of the pulmonary Circulation in As- 

 phyxia ( 574), but by the curious fact ascertained by Dr. J. Reid, 3 that the blood, 

 when imperfectly arterialized, is retarded in the systemic capillaries, causing an 

 increased pressure on the walls of the arteries. He found that, when the in- 

 gress of air through the trachea of a Dog was prevented, and the Asphyxia was 

 proceeding to the stage of insensibility the attempts at inspiration being few 

 and labored, and the blood in an exposed artery being quite venous in its cha- 

 racter the pressure upon the arterial walls, as indicated by the hsemadynamo- 

 meter applied to the femoral artery, was much greater than usual. Upon ap- 

 plying a similar test to a vein, however, it was found that the pressure was 

 proportionably diminished; whence it became ' apparent, that there was an un- 

 usual obstruction to the passage of venous blood through the systemic capilla- 

 ries. After this period, however, the mercury in the hsemadynamoineter 

 applied to the artery began to fall steadily, and at last rapidly, in consequence 

 of the diminished force of the heart, and the retardation of the blood in the 

 pulmonic capillaries ; but, if atmospheric air was admitted, the mercury rose 

 instantly, showing that the renewal of the proper chemical state of the blood 

 restored the condition necessary for its circulation through the capillaries. 4 



527. It appears, from the preceding facts, that the conditions, under which 

 the power in question uniformly operates, may be thus simply and defi- 

 nitely expressed: Whilst the injection of blood into the Capillary vessels of 

 every part of the system is due to the action of the Heart, its rate of passage 

 through those vessels is greatly modified by the degree of activity ii^the 

 processes to which it should normally be subservient in them; the current 

 being rendered more rapid by an increase in their activity, and being stagnated 

 by their depression or total cessation. Or at any rate, to use the more guarded 

 language of Mr. Paget (loc. cit.), "we have facts enough to justify such an 

 hypothesis, as that there may be some mutual relation between the blood and 

 its vessels, or the parts around them, which, being natural, permits the most 

 easy transit of the blood, but, being disturbed, increases the hindrances to its 



1 "Brit, and For. Med. Review," vol. xiv. p. 600. 



2 See Mr. Paget, loc. cit., p. 971. The Author had long previously satisfied himself 

 that such was the fact ; and is glad to be able to cite the far more extended observations 

 of Mr. Paget on this point, in confirmation of his own. 



' 3 "Edinb. Med. and Surg. Journ.," April, 1841; and "Anat., Phys,, and Pathol. Re- 

 searches," chap. ii. 



4 This last fact (as Dr. Eeid has remarked) is sufficient to negative the idea of Mr. 

 Erichsen, that the obstruction is caused by the contraction of the capillaries under the 

 stimulus of venous blood ("Edinb. Med. and Surg. Journal," Jan., 1845) ; for all experi- 

 ments agree in showing that such contraction can only be excited by the application of a 

 stimulus for some minutes, and that relaxation takes place still more slowly ($ 513). 



