494 APPENDIX. 



with others, incline me to believe that this crystalline substance is 

 not a mixture of a pigment and a protein-body, but a pure 

 chemical compound; the difference in the form of the crystals of 

 different kinds of blood seems to indicate with tolerable certainty 

 that this compound must, however, be either a salt-like or a con- 

 jugated compound. All the analyses which I have hitherto made 

 of the pure substance have failed, like all previous elementary 

 analyses of the protein-bodies, in yielding any definite views as to 

 the constitution of this substance, but it seems to me that its 

 recognition is rendered very simple on the supposition of a con- 

 jugation ; the principal object to be had in view is, therefore, to 

 discover some agent which will dissolve this conjugated compound^ 

 and separate the substance into its adjuncts ; in how far I have 

 succeeded in this purpose, I am scarcely able to determine. If 

 the somewhat irrelevant question were asked, whether the crystal- 

 line substance is contained as such in the blood-corpuscles, existing 

 in it only in a dissolved form, I could not directly affirm that such 

 is the case, for the influence of such forces as light and oxygen, 

 which are necessary to the formation of crystals, is inconceivable 

 without the co-operation of chemical action : hence we might be 

 led to assume that an oxidation had previously taken place. As, 

 however, crystals cannot be formed without the co-operation of 

 carbonic acid, mere oxidation cannot constitute the sole form of 

 metamorphosis of the substance, for carbonic acid must essentially 

 contribute towards the production of the new substance, which is 

 then first rendered crystallisable. It might naturally be supposed 

 that the investigation of this subject would enable us to decide 

 the much disputed question of the interchange of gases in the 

 circulating blood, but the decision of this point is by no means so 

 easy as we might be disposed at first sight to assume ; at all 

 events, owing to the small quantity by weight which is taken up 

 by this substance, I have hitherto been unable to obtain any 

 reliable results from my own quantitative determinations ; other 

 essential obstacles, moreover, hinder the determination of the gas 

 which is to be absorbed. It must, moreover, be borne in mind 

 that this capacity of the crystalline substance to be changed by 

 the action of oxygen and carbonic acid is not peculiar to this body 

 alone, but pertains without exception to nearly all the protein- 

 bodies, as indeed every careful observer must have noticed, and as 

 I have myself observed in the case of albumen, casein, globulin, 

 &c., when submitted to a similar treatment with oxygen and 

 carbonic acid. All protein- bodies undergo essential alterations in 



