PREVIOUS TO THE INVESTIGATIONS OF PREYER. 91 



also noted independently of Hoppe-Seyler the feeble state of the combina- 

 tion of the oxygen, for he notes that shaking the blood with CO 2 removes 

 the O, and he states that if, as we have reason to believe, this oxygen is 

 for the most part chemically combined, it follows that carbonic acid acts 

 as a reducing agent, and that we are led to regard the change of color not 

 as a direct effect of the presence of carbonic acid, but a consequence of the 

 oxygen. He records certain differences between effects of carbon dioxide 

 and the "real" reducing agents, and he notes that while the former no 

 longer acts on a dilute and comparatively pure solution of scarlet cruorin, 

 the latter acts just as before. He infers that scarlet cruorin is not merely 

 a greedy absorber and carrier of oxygen, but also an oxidizing agent, and 

 he states that "as the purple cruorin in the solution was oxidized almost 

 instantly on being presented with free oxygen by shaking with air, while 

 the tin solution remained in an unoxidized state, so the purple cruorin 

 of the veins is oxidized during the time, brief though it be, during which it 

 is exposed in the lungs, while the substance derived from the blood may 

 have little disposition to combine with free oxygen. As the scarlet cruorin 

 is gradually reduced, oxidizing thereby a portion of the tin salt, so part of 

 the scarlet cruorin is gradually reduced in the course of the circulation, 

 oxidizing a portion of the substances derived from the food or of the tis- 

 sues; the purplish color now assumed by the solution represents the tinge 

 of venous blood, and a fresh shake represents a fresh passage through the 

 lungs." 



Immediately following Stokes's article a contribution by Hoppe-Seyler 

 appeared (Centralblatt f. med. Wissensch., 1864, n, 817, 834) in which he 

 refers to the work of Stokes as follows: "The observation of Stokes coin- 

 cided fully with my observation earlier, but in addition there are phenom- 

 ena described by him with which I was already familiar, but only showed 

 in my lectures." The author then makes reference to various experiments 

 he had carried out in this particular direction of inquiry, and also in con- 

 nection with hematin. 



Kuhne (Archiv f. path. Anat. u. Physiologic, 1865, xxxm, 79) iden- 

 tified the spectrum of the coloring matter of muscles with that of the blood 

 described by Hoppe-Seyler. In a later article (ibid., xxxiv, 423) he reports 

 having crystallized reduced hemoglobin. He made a concentrated solution 

 of crystals of dog's blood in very weak ammonia, and then subjected the 

 solution in a gas chamber to pure dry hydrogen. Crystallization occurred 

 as evaporation proceeded. Oxyhemoglobin of the dog, he notes, is very 

 insoluble, while the reduced hemoglobin is very soluble, and he points 

 out that the difficulty experienced in preparing reduced hemoglobin crystals 

 is owing to their great solubility. He also noticed intraglobular crystal- 

 lization. Rollett (Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1866, LII, 2 

 Abth., 246) shortly afterward prepared reduced hemoglobin crystals by 

 agitation with reduced iron. Schultz had (Archiv f. mikros. Anat., 1865, 

 xxxi, 1) the year before reported crystals of monkey's blood which he 

 obtained by the addition of water and alcohol to the blood, and which 

 were doubtless reduced hemoglobin. 



