522 APPEiNDIX. 



absorbing power of the fluid cannot be referred to any cause but 

 chemical attraction. Although, in the case of the oxygen, we are 

 not so well acquainted with the matters which retain it, as with 

 those which are able to fix the carbonic acid 'in the blood 

 (alkaline carbonates, phosphates, &c.), the proposition is almost 

 equally established for both cases, that the excess of carbonic acid 

 and oxygen which the blood is able to absorb beyond the amount 

 which corresponds to the quantity of water which it contains, must 

 be present in the blood in a state of chemical combination. We 

 have already endeavoured to show (in vol. i ? p. 439) that the 

 possibility of breaking up such an unstable combination by the aid 

 of other indifferent gases (as hydrogen, &c.) furnishes no evidence 

 against the fact that the expelled gas has been chemically com- 

 bined. Liebig is therefore certainly in the right when he ad- 

 vances the proposition, that a gas can only be considered as 

 mechanically absorbed when its quantity increases and diminishes 

 in proportion to the external pressure. We think we are justified 

 in concluding with Liebig, that the quantity of oxygen which may 

 be absorbed by the blood is constant in amount, and to a certain 

 extent independent of external pressure, an opinion which is 

 based partly upon the fact, that the respiratory process is carried 

 on nearly the same, both at very great heights and at the level of 

 the sea, and that no more oxygen is absorbed even in an air very 

 rich in oxygen than in the ordinary atmosphere. 



In addition to these physical proofs in favour of the chemical 

 absorption of the oxygen in the blood, I may perhaps be permitted 

 to refer to the following experiments, instituted by myself, with 

 the pure crystalline substance of the blood, although they can 

 scarcely be said to furnish any conclusive result. A perfectly 

 limpid saturated solution of pure blood-crystals, which was not 

 precipitable either by nitrate of silver or by basic acetate of lead, 

 and which was of a beautiful pomegranate-red colour, was 

 saturated, one part with carbonic acid and another with oxygen ; the 

 oxygenous fluid exhibited no remarkable difference of colour from 

 the original fluid, which was contained in a similar vessel ; more- 

 over, no distinct difference of colour could be perceived between 

 the solution which was impregnated with carbonic acid and the 

 normal fluid, or the solution impregnated with oxygen ; but 

 ;he solution of the blood- crystals through which carbonic acid 

 had been passed was somewhat turbid and exhibited under the 

 microscope large numbers of faintly granulated flakes. In vacuo 

 the latter fluid developed a very large amount of gas, and 



