226 Analyses of Books. 



from blood, under the exhausted receiver of an air pump, and also, 

 that of Brande, who obtained 2 cubic inches of acid from 1 ounce of 

 both arterial and venous blood. Dr. Davy could detect no such evo- 

 lution, and Gmelin and Tiedemann could not succeed unless after the 

 addition of acetic acid. Now, what conclusion should be drawn from 

 this variety of results ? Two only appear to us admissible, either, that 

 blood, in some cases, does contain carbonic acid, and in others does not ; 

 or, that the experiments had been performed under different circum- 

 stances. According to Dr. Stevens, no carbonic acid is given out from 

 venous blood by the mere removal of pressure ; but, when two vessels 

 are employed (one filled with hydrogen, and containing some blood, 

 and communicating with another by means of a bent tube dipping into 

 barytes water), and then the whole placed in an exhausted receiver, 

 so that the hydrogen and whatever gas may be evolved from the 

 blood passes through the alkaline solution, he found that a pre- 

 cipitate was always produced in the latter. We have no proof, it is 

 to be regretted, from the mode in which the experiment is detailed, 

 that the hydrogen contained no carbonic acid, or, that the precipitate 

 was a carbonate. But there is nothing new in all this, for Vauquelin, 

 long ago, stated, that blood, placed in hydrogen, evolved carbonic 

 acid. We observe, that the author claims the discovery of the diffu- 

 sive power of oxygen in reference to other gases, as exemplified in 

 the case of hydrogen in the experiment described by him. But the 

 fact is, that Mr. Dalton, long ago, broached the subject of the 

 mechanical mixture of the gases generally, while Mr. Graham dis- 

 covered the law of their diffusibility, viz., by the interchange of 

 indefinitely small volumes of the gases, inversely proportional to 

 the square root of their densities. 



Having proved that carbonic acid exists in venous blood, the author 

 concludes, that the latter derives its dark colour from the presence 

 of that acid. Now, what can be more fallacious than such a con- 

 clusion, until it has been determined that arterial blood contains no 

 carbonic acid ? especially, when, according to Mr. Brande's experi- 

 ments, it appears that from both kinds of blood carbonic acid can be 

 extracted. The author then proceeds to support the common theory 

 of respiration by the absorption of oxygen, and the evolution of car- 

 bonic acid by the venous blood in the lungs. Some of the hypotheses, 

 which he brings forward are amusing enough. For example, he 

 supposes that the globules, which are observed to leave the tissue 

 surrounding the extreme arteries after the blood has left the latter, 

 are minute particles of oxygen, and that the globules which return 

 are minute particles of carbonic acid; but judiciously adds "this 

 cannot be easily pr wed." Such speculations might have suited the 

 pages of some ephemeral publications, but should not have been in- 

 troduced into those of the Philosophical Transactions. 



Discovery of the Metamorphosis in the second type of the Cir- 

 ripides, viz., the Lepades, completing the natural history of these 

 singular animals, and confirming their affinity ivith the Crustacea. 

 By J. V. Thompson, F. L. S. 



