rather large, render this sort of comparison very easy. I perceive that we cannot infer from what takes place in the intestines, what happens in the pituitary, palatine membrane, &c. because though analogous, the organization may be different. We cannot here as in the intestines examine the venous blood returning from the part; but, 1st, if we consider that in animals who have respired oxygen for some time, we see the palatine and pituitary membranes more red; 2d, if we reflect that the lividity of the different parts of this membrane, in those destroyed by asphyxia by the carbonic acid gas, depends not on the immediate contact of this gas upon the membrane, but upon the passage of venous blood into the arterial system, as my experiments have, I think, demonstrated; 3d, if we remark finally that in these circumstances the contact of the air does not change, after death, the lividity which the venous blood gives to the mucous membranes, although the skin be then much more permeable to every kind of aeriform fluid; we shall see that it is at least necessary to suspend our judgment upon the colouring of the blood in the mucous membranes, until further observations have decided the question. The following experiment may also throw some light upon the subject. I have inflated the peritoneal cavity of several guinea-pigs with carbonic acid gas, with hydrogen, oxygen and atmospheric air, to see if I could effect through a serous membrane what I could not make succeed in a mucous; I have not, after these experiments, found any difference in the colour of the blood of the abdominal system; it was always the same as in the common guinea-pig which I killed for comparison. I think however that I have remarked many times, both in frogs and animals with red and warm blood, such as cats and guinea-pigs, that the infiltration of oxygen into the cellular texture gives, at the end of some time, a much brighter colour to the blood, than that which this fluid exhibits in artificial emphysemas produced by carbonic acid gas, hydrogen and atmospheric air, in all which the colour of the blood scarcely differs at all from what is natural. But in other cases oxygen has had no influence upon the colour of the blood; so that notwithstanding having made many experiments upon this point, I am unable to give any general result. It appears that the tonic forces of the cellular texture and of the parietes of the vessels which are spread upon this texture, receive a very variable influence from the contact of the gases, and that according to the nature of this influence, the fibres crisping and contracting more or less, render these parts more or less permeable, either to the aeriform fluids that tend to escape from the blood in order to unite with that of the emphysema, or to this last fluid, if it tends to combine with the blood, which no doubt produces the varieties I have observed.