ADDITIONS AND NOTES TO VOL. II. 523 



retained its turbidity and colour ; these flakes remained unchanged 

 when seen underthe microscope. Both the normal fluid and the fluid 

 impregnated with oxygen remained unchanged both as to colour and 

 clearness in vacuo, although they developed relatively less gas. 

 When the solution of blood-crystals was first saturated with 

 oxygen, and then exposed to a stream of carbonic acid, the fluid 

 became turbid without any marked changed of colour, and ex- 

 hibited the same flakes under the microscope as the solution 

 which had been treated directly with carbonic acid. If, however, 

 a stream of oxygen be suffered to pass through the fluid, which 

 has been rendered strongly turbid by carbonic acid, it at once 

 becomes perfectly limpid without exhibiting any perceptibly 

 increased lightness of colour. The substance may be again ob- 

 tained in a crystallised form and unchanged, both from the turbid 

 solution charged with carbonic acid and the clear fluid to which 

 oxygen has been added. This separation of solid molecules by 

 carbonic acid might seem to present a strong indication of a 

 chemical action of the gases, but it could not be made to corre- 

 spond with the opinion of Bruch,* that the normal colour of the 

 substance in question is developed in the presence of carbonic 

 acid. Other gases than oxygen and carbonic acid evidently exert a 

 chemical action, like dilute organic acids, alkalies, &c. ; this, for 

 instance, is the case with carbonic oxide, for it not only very con- 

 siderably darkens the deep red solution of the pure crystals, but it 

 also gives rise to a dark brownish red coagulum (which exhibits 

 great variety of form when seen under the microscope). Neither 

 solutions of the original colour, nor crystals, can be procured 

 from this fluid, either by repeated treatment with oxygen, or with 

 carbonic acid and oxygen. Nitrous oxide renders the red fluid 

 darker, almost brownish red, and very turbid, so that the microscope 

 exhibits the whole fluid as if it were filled with flakes ; neither 

 oxygen nor carbonic -acid restores the clearness or the original 

 colour of the fluid, for the greater part of the substance crystallises 

 unchanged. (Nitrous oxide may, therefore, be employed in the 

 place of the oxygen in the mode of preparing the crystalline sub- 

 stance of the blood described at p. 491 of this volume, but it cannot 

 take the place of the carbonic acid.) There can scarcely, therefore, be 

 any doubt that the gases (oxygen and carbonic acid) exert a chemical 

 action upon the colouring principle of the blood-corpuscles, as we see 

 from these experiments, as well as from the entire mode of pre- 



* Zeitsch. f. rat. Med. Bd. 1, S. 440-450, Bd. 3, S. 308-318, and Zeitsch. f. 

 wissensch. Zoologie. Bd. 4, S. 373-376. 



