478 ' CHEMISTRY OF THE PROTEIDS CHAP. 



globin derivatives to be mentioned later on : methsemoglobin and 

 haemin are dark blackish brown and pale yellowish brown ; methsemo- 

 globin, in crystals, is colourless ; CO-hsemoglobin is purple and 

 white. According to the axial plane they affect the spectrum in a 

 different manner, as the absorption-bands become shifted either towards 

 the red or towards the violet end of the spectrum. Ewald draws 

 attention to the fact that similar phenomena are also observed if a 

 substance be dissolved in media possessing different dispersions, and 

 points out what care is required in interpreting small spectroscopic 

 differences such as are shown by the haemoglobin derivatives under 

 different conditions. 



Blood crystals are denaturalised and are converted into pseudo- 

 morphoses on being kept, or on being allowed to dry, or when acted 

 upon by alcohol, but their power of refracting light doubly they may 

 retain for a considerable time. 1 Crystals which have become insoluble 

 owing to the action of alcohol, but which still give the typical 

 spectrum and which are still doubly refractile, Nencki 2 has called 

 1 parahsemoglobin.' 



The Gaseous Compounds of Haemoglobin and its 

 Optical Properties 



During its passage through the lungs the blood of vertebrates 

 becomes saturated with oxygen, and during its passage through the 

 rest of the body it parts with this oxygen, which is taken up by 

 the tissues; arterial blood, containing oxygen, is of a bright-red colour, 

 while venous blood, poor in oxygen, is of a darker-red, and even purple 

 colour ; in cases of asphyxia the blood is almost black. A solution of 

 haemoglobin on being brought together with atmospheric oxygen 

 absorbs one molecule of oxygen for each molecule of haemoglobin, and 

 becomes converted thereby into oxyhsemoglobin. The chief character- 

 istic of the two haemoglobins, namely, of oxy- and reduced haemo- 

 globin, is their absorption-spectrum; Hoppe-Seyler 3 was the first to 

 describe the spectrum of oxyhsemoglobin, while Stokes 4 first prepared 

 and studied the reduced hemoglobin. 5 The best method for reducing 



1 W. Preyer, Blutkristalle, Jena, 1871. 



2 M. Nencki, Schmiedeberg's Arch.f. exper. Pathol. u. Pharmak. 20. 332 (1885). 



3 F. Hoppe-Seyler, Virchow's Archw. 33. 446 (1862) ; Zentralbl. f. d. med. Wissen- 

 sc/iaften, 1864, pp. 261, 817, 834 ; Med.-chem. Untersuch. p. 169 (1867). 



4 G. G. Stokes, Philosoph. Magazine and Journ. of Science, 27. 4th Ser. p. 388 

 (1864) ; Proc. Roy. Soc. 1864, June 16 (according to Neumeister's textbook). 



5 Stoke's solution for reducing haemoglobin is prepared as follows : Two grams of 

 ferrous sulphate are dissolved in 100 cc. of a 3 per cent watery solution of tartaric acid, 



