6. That in the production of new vessels which occurs in adhesion or granulation, the new blood executes oscillatory motions in the rudimentary vessels while in the act of form ing, before these parts of vessels are connected with the previously existing branches through which the heart propels the blood; and this is said also to occur in the formation of new ves sels in natural growth.'* 7. That in the formation of the vascular area of the incubated egg the blood moves in part through the veins and small vessels before it is impelled by the action of the heart.t We would remark, regarding the oscillatory and irregular motions described by Haller and others as occurring in the small vessels of the web after removal of the heart or ligature of the aorta, that we believe some of these to be caused by the elasticity of both the arteries and veins, and others to be occasioned by the 0-radual or tonic contractions which take place in the arteries after death :I they occurred in all Haller's observations, but in Spallanzani's only when the apparatus of hooks constantly em ployed by Haller was applied; and so far as we have ourselves been able to observe them, we have always found them influenced by very slight changes. When one of the small vessels is obstructed they cease altogether, which ought not to be the case were they dependent upon powers belonging to the capillaries or the blood in them. Some varieties in the velocity and di rection of the blood in the smaller vessels we have reason, from our own observations, to attribute to the same causes, and we think it consonant with such a supposition that heat or other agents influencing the contraction of arteries should influence these irregular mo tions. The oscillations of blood in parts of vessels which are in the process of formation in adhesions and granulations, or in natural growth, we have not yet been able to observe so clearly as to be certain that we were not de ceived but, even supposing them to have been satisfactorily proved to occur, we should be inclined to doubt the possibility of ascer taining with accuracy that these. portions of vessel are entirely shut off from all commu nication with other vessels, so as that no im pulse could be transmitted from the heart to them. The necessity of some change in the tissue of organs or of organizable lymph, in which new vessels are about to be formed before the propulsion of the blood into the new loop of vessel seems sufficiently obvious, but it does not appear to be as yet satisfactorily shewn that the motion of blood in the new vessels is independent of a propulsion received from the heart. Again we consider it as ascer tained that the heart of the chick acts just as soon as any motion of fluids can be seen on the vascular area of the yolk ; and though it may be admitted that a certain change of place in the particles of the yolk is necessary in the new combinations which occur during the de velopmen t of the forming parts from its substance, yet such a change or motion must be quite of an insensible kind and not in any degree ana logous to the continued stream of circulating; blood through the vessels.
The stagnation of venous blood in the Capil laries of the lungs is certainly a most remark able and inexplicable phenomenon, but if from analogy any weight is to be attached to obser vations made upon the frog, it may be stated that the flow of blood through the lungs seems as immediately dependent on the heart's action as that through the system. The portal circu lation is not more remarkable in respect of its isolation from the heart than the systemic cir culation of fishes,. in which animals the capil laries of the gills intervene between the heart and the systemic aorta; and without any dis tinct contraction of that vessel, the circulation of the blood in the systemic capillaries as well as in the gills is very manifestly main tained chiefly, if not solely, by the action of the heart. We do not feel inclined to attach
any importance to the alleged motions of the globules of the blood out of the vessels, for we have never been able to see any such in dicating different powers from those which produce currents in inorganic fluids, and some of the observations upon which the statement is founded have been shewn to be erroneous.
We think it unnecessary to do more than merely to allude to some of the very many attempts that have been made to account for independent motion of blood in the capillaries, or what have been termed the theories of the capillary circulation.
All that we know of capillary attraction mi litates against the possibility of its being the means of causing a progressive motion of fluids, such as that which occurs in plants and ani mals. Those who have attributed the motions of fluids in the living body to endosmosis or a principle of organic transudation, have failed in pointing out in the bloodvessels the condi tions necessary for the occurrence of a motion proceeding from an action of this description. The electrical theory is defective in this essen tial point, that no difference in the electrical condition of the arterial and venous blood has been shewn, and that the same cause to which the motion of the capillaries of the systemic arteries is ascribed ought to retard the passage of blood in the pulmonary capillaries, the re lations of the two kinds of blood being there reversed. The opinion that the motion of the blood in the vessels is analogous to those cur rents of fluids which take place in contact with the surfaces of various parts of anitnals, which are almost always connected with ciliary mo ti ons, and are described under the head of CILIA in this Cyclopedia, isdefective in so far as neither cilia nor any power of exciting currents has yet been shewn to exist in the interior of the bloodvessels, and they have been examined in circumstances in which we conceive they would have been seen had they been present. In fine we cannot see how any power of spontaneous motion belonging to the blood itself could be a cause of progressive motion of that fluid, unless the direction of the motion were determined by the solid textures containing the blood, and in this case the same objections would apply to this explanation of the cause of motion as to the one to which allu sion has just been made; and besides, the evi dence of spontaneous motions of the blood ap pears upon the whole of a very unsatisfactory k ind.
From these considerations we find ourselves constrained to hold the opinion that, however great the power which the capillary vessels possess of modifying the distribution of the blood, there is not reason to believe that they contribute as a whole to its progressive motion.
4. Phenomena of the venous circulation.—ln the natural state of the circulation the flow of the blood is nearly quite uniform in the veins, as may be seen when a vein is opened in the common operation of venesection. In those rare instances in which the flow from a vein is accelerated after each beat of the heart, in the same way as the arterial jet, it may be supposed either that the intermitting impulses of the heart are, from some circumstance or other, transmitted more freely and to a greater dis tance than usual through the capillary vessels, as is known occasionally to happen, or, what is more probable, that the larger branch of the vein receives the successive impulses directly from neighbouring large arteries, which are more than usually dilatable.