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little of carbonic acid. Other physiologists, taking for starting point the fact of the excess of the consumption of the oxygen over the production of the carbonic acid, they admitted a variant of the hypothesis of the combustion of Lavoisier, accepting the formation of the carbonic acid in the lung, but denying the one of the aqueous vapors, and adding that the remaining oxygen of the formation of the acid combines with the blood, it modifies its coloration, and that the globules, in accordance with the combined oxygen, they will excite the life of the organic parts. Opinion ahead of time defeated by the refutation of the primitive one. Lagrange and Hassenfratz also adopted another variant of the combustion, changing its seat. They gave in the lung the simple combination of the oxygen with the blood, and then, in the continuation of the circulation, its combination with the carbon, resulting the acid that, absorbed then by the blood, it came to free itself in the lung. This variant enjoyed a lot of acceptance, because the H. Davy's experiences demonstrated the existence of the carbonic acid, although in small amount in the arterial blood, and the one of Voguel, Home and other the same, but in big, in the veined one. Stevens established an all private theory in that he denied to the oxygen all and any part in the color change that suffers the blood in the breathing, only attributing it to the descarbonization. He was founded in that the neutral salts turn the blood rutilant, but that the carbonic acid surely grows dark, it seems, forming a super-salt. He wanted the dark red color be own of the coloring matter of the blood, which changed for the action of the neutral salts dissolved in the serum; but that the birth, in the general capillary system, of the acid carbonic restored it, and that the exhalation of this in the lung allowed the salts of the serum to continue its action and effects. False theory, not only because the descabornization is insufficient, when isolated, to change the sanguinous coloration, but also because, as in time one will see, it is mainly the oxidation that determines it. Firming himself in experiences of Spallanzani repeated by Edwards, that prove the continuation of the production of the carbonic acid in the animals of cold blood, even breathing an air naked of oxygen, other founded the theory, that the breathing consists of a secretion formed in the lungs at the expense of the materials supplied by the blood, as well as any other one secretion. This theory falls due to the demonstration of the preexistence of the carbonic acid in the veined blood. A complicated theory was established by Mitscherlich, Gmelin and Fiedman, that, besides ingenious, seemed to give explanation of the facts, by which it obtained great favor, while it was not known the already mentioned, and proven by the same Gmelin, preexistence of the carbonic acid in the blood still non arterialized. They founded these wise persons their theories in the preexistence, not of the carbonic acid, but of the acetic acid, or of the lactic, free or combined, in most of the secretions and of the blood; and which; not penetrating in the victuals already formed in enough amount to supply what of continuous leaves for the urine and sweat, it should be engendered even in the animal body. Besides that,