In the normal state, the membranous vesicle of the globules of the blood appears perfectly smooth among vertebrate animals; but among the invertebrata its surface is uneven and modulated like that of a raspberry, as we have already said. ffewson, however, observed that when the blood of the vertebrata began to putrefy, the globules then presented an appearance analogous to what we have remarked in those of the crustacea and mollusca. In the mammalia the central nucleus is circular and depressed, and in all this class of animals it appears to be similar in size. In the oviparous vertebrata, it is on the contrary elliptical in figure, though, according to Messrs. Prevost and Dumas, it acquires this figure in consequence. of a par ticular substance being fixed around it, itself being in reality circular, as among the mam malia.
It frequently happens that other smaller corpuscles than the globules of which we have treated hitherto are observed swimming in the serum. These are of a whitish colour and simi lar to the molecules that occur in almost all the fluids of the animal economy. The resem blance that exists between these corpuscles and the central nuclei of the proper globules of the blood might lead to the belief that they were nothing more than the central nuclei divested of their coloured envelope ; but in several of the inferior tribes, as the river-crab and certain mollusca, in the blood of which they occur in very considerable numbers, the central nuclei of the globules are much larger, and it is impossible to confound the two toge ther. These then are to be regarded, not as globules of the blood, properly so called, altered in any way, but as globules of albumen or fibrine. These substances, in fact, have always the appearance of being made up of circular corpuscles of extreme minuteness when by any means they are brought into the solid state ; and we are led to believe that even when dissolved or suspended in water they still preserve this peculiar disposition, and only escape detection under the microscope by their dissemination and transparency.
To recapitulate, then, we find :— 1st. That the globules of the"blood are mem branous sacs inclosing a solid flattened nu cleus in the form of a disc, in their interior.
2d. That their form and their dimensions vary among animals of different species, but that in the same animal they all bear the strongest resemblance to one another.
3d. That in the mammalia these corpuscles are circular and smaller than in any other class of animals.
4th. That in birds the globules of the blood are elliptical and larger than in the mammalia; their dimensions vary slightly in different genera, but this variety does not seem to ex tend further than to the admeasurements of their long diameters.
5th. That in vertebrate animals with cold blood the globules are also elliptical, but that their dimensions are much greater and vary more extensively in different classes ; reptiles, more especially the batrachia, are of all animals those in which the globules of the blood are the largest.
6th. That in the invertebrata the globules of the blood are more or less regularly circular in shape, and are also of very considerable dimen sions.
It appears to be especially owing to the presence of the globules, the common physical properties of which we have thus far studied, that the blood owes its power of arousing and keeping up vital motion in the animal economy. We observe, in fact, that if an animal be bled till it falls into a state of syncope, and the further loss of blood is not prevented, all muscular motion quickly ceases, respiration is suspended, the heart pauses from its action, life is no longer manifested by any outward sign, and death soon becomes inevitable ; but if, in this state, the blood of another animal of the same species be injected into the veins of the one to all appearance dead, we see with amazement this inanimate body return to life, gaining accessions of vitality with each new quantity of blood that is introduced, by-and bye beginning to breathe freely, moving with ease, and finally walking as it was wont to do, and recovering completely. This operation, which is known under the name of transfusion, proves better than all that can be said the importance of the action of the globules of the blood upon the living tissues; for if, instead of blood, serum only, deprived of globules, be employed in the same manner, no other or further effect is produced than follows the in jection of so much pure water, and death is no less an inevitable consequence of the he morrliage.
A variety of other experiments upon trans fusion, for which we are equally indebted to Messrs. Prevost and Dumas, show the influence which the form and volume of the globules of the blood exert upon its physiological proper ties. if the blood introduced into the veins of a living animal differs merely in the size, not in the form of its globules, a disturbance or derangement of the whole economy more or less remarkable supervenes. The pulse is in creased in frequency, the temperature falls rapidly, the alvine evacuations become slimy and sanguinolent, and death in fine generally happens after the lapse of a few days. The effects produced by the injection of blood having circular globules into the veins of an animal the globules of whose blood are ellip tical, (or vice versa,) are still more remarkable ; death then usually takes place amidst nervous symptoms of extreme violence, and comparable in their rapidity to those that follow the intro duction of the most energetic poisons.