MOVEMENT OF THE BLOOD IN THE CAPILLARIES. 351 



blood may be affected by any agency which alters the cJiemico-vital relations 

 between the blood and the tissues which it permeates. Thus, when the in- 

 terrupted electric current was applied to the Capillaries by the Profs. Weber, 

 they noticed that the blood-corpuscles showed a remarkable tendency to ad- 

 here to each other and to the walls of the vessels, so as to produce a great 

 amount of friction and a consequent retardation. 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 Inflammation in it, produces a like stagnation. This effect cannot 

 be attributed to mechanical obstruction in the vessels, for they are usually 

 dilated rather than contracted, when this condition exists; and without any 

 change in the dimensions of a tube, the stream of blood through it may be 

 seen decreasing from extreme velocity to complete stagnation. 2 That altera- 

 tions in the chemical state of the blood (involving, of course, 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 Asphyxia, but by the curious fact ascer- 

 tained by Dr. J. Reid, a 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 ingress 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 character, the 

 pressure upon the arterial walls, as indicated by the hremadynamometer ap- 

 plied to the femoral artery, was much greater than usual. Upon applying 

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

 tionably diminished; whence it became apparent, that there was an unusual 

 obstruction to the passage of venous blood through the systemic capillaries. 

 After this period, however, the mercury in the hseraadynamoineter 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 

 i)i*tntly, showing that the renewal of the proper chemical state of the blood 

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

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

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

 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 in 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 stag- 

 nated 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 

 the hypothesis, "that there is some mutual relation between the blood and 



1 Brit, and For. Mod. Review, vol. xiv, p. 



2 bee Mr. Paget, Op. cit., p. 311. The Author hud long previously satisfied him- 

 self that such was the fact; and is glad t<> be ahle to cite the far mure extended ob- 

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



3 Edinb. Med. and "burg. Journ., April, 1841 ; and Anat., Phy.*., and Pathol. Re- 

 searches, chap. ii. 



4 This last fact (as Dr. Reid 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 burg. Journ., Jan. 1845) : for all experi- 

 ments agree in showing, that such contraction can only be excited by the applica- 

 tion of a stimulus for some minutes, and that relaxation takes place still more slowly. 



