The experiments of Brande" would, however, lead to a different conclusion ; he sheaved that the air contained in the blood had much in fluence in the formation of bloodvessels. This air is carbonic acid gas, and its quantity appears to be nearly equal in the two kinds of blood ; being estimated at a cubic inch for every ounce of blood. This gas may be separated from the blood by the air-pump, and it escapes with a kind of bubbling or effervescence, causing the ascent of the mercury in a barometer attached to the apparatus.
It has been remarked that during the coagu lation of the blood, a large quantity of carbonic acid gas escapes ; this coagulation, observed under the microscope, has shewn that the gas, by escaping in all directions, forms a net-work of canals, the branches of which anastomose with each other ; and that this net-work pre serves its form after desiccation. It has also been established that it is this gas which forms those canals in coagulated blood ; because, if by means of the air-pump we deprive the blood of it, before it is coagulated, they do not occur.
Sir E. Home has even injected the vessels which were developed in the coagulum soon after the blood was taken from a vein. If the formation of new vessels occur even in a coa gulum of blood removed from the living body, but preserving still a certain quantity of its heat, and of its vitality, with more reason might we expect that a similar phenomenon should obtain during life : and this fact has been de monstrated by experiments performed on a rabbit, in which had been produced a hemor rhage from a small branch of the mesenteric artery : after twenty-four hours, the coagulum which was formed was injected.
The formation of vessels in coagulated blood, by means of the carbonic acid gas which tra verses it in all directions, is in perfect accord ance with the observations which have been made by M. Bauer upon germinating wheat, which were instituted for the purpose of skewing the influence of the globule of air. These globules are manifested below a bud of mucilaginous substance ; they push it forward, elongate it, and thus form a filament.
I do not, however, believe that either of these theories correctly explains the pheno menon.
It was for a long time believed that false membranes were never organised ; that nature had given to the parts of our economy an almost unlimited power of development, but not the faculty of communicating life to the products of the circulation ; that false mem branes appeared to be organised 'only because they constituted a kind of frame-work through which vessels from the inflamed tissue might be prolonged : ulterior observations, however, have shewn that these media are really or ganised. We have no general rules as to the
time when such organisation shall commence. It seems to be dependent upon inexplicable individual dispositions. It may, however, be remarked, that the greatest analogy exists be tween the mode of development of vessels in these of adhesion and their mode of production in the membrane of the yolk in the chick, saving always this remarkable circum stance, namely, the inconstancy, the irregu larity of the work of organisation in the former, and, on the contrary, the constancy and the regularity of the occurrence in the latter case.
These media are in fact secreted by a tissue, the vitality of which is exalted to a certain extent, and it appears to impress upon the pro duct of its secretion a commencement of vitality, as in generation. All these circumstances ap pear to me that these vessels are the product of a spontaneous generation—a true epigenesis ; so indeed, to a certain extent, thought Hunter. He says, " In a vast number of instances I have observed, that in the sub stance of the extravasation there were a great number of spots of red blood, so that it looked mottled. The same appearance was very ob servable on the surface of separation between the old substance and the new, a good deal like petechial spots. Was this blood extra vasated along with the coagulating lymph ? In this case I should rather have supposed it would have been more diffused. I have there fore suspected parts have the power of making vessels, and red blood, independent of the circulation." If the inflammation be not strictly confined to that state in which the albumino-fibrinous exhalation is accomplished, but proceeds to the next stage, the exhalation entirely changes character ; pus is produced, a granulating sur face is developed, and union is accomplished by the intervention of another tissue, and by a slower process than that which we have already described. This is the process which is always observed in mucous membranes, scarcely ever in serous; for in the former, the albumino-fibri nous matter never becomes organised, and can therefore never be the medium of a permanent union. In these membranes, if adhesion occur, the inflammation must proceed to the succeed ing stage. Adhesion of mucous membranes, however, does not often occur—it is not com patible with the performance of their functions.