VISIBLE SPECTRUM OF OXYH^MOGLOBIN. 209 



many persons of distinction in all countries, amongst the first and most 

 successful of whom were W. Preyer 1 in Germany, and Sorby and Ray 

 Lankester in England. Amongst all, however, who by their work have 

 contributed to the spectroscopic investigation of the blood, two appear to 

 me to stand out pre-eminently these are Vierordt and Hiifner. By the dis- 

 covery of the first practical method of determining the extinction-coefficient 

 of coloured liquids, and his elaboration of a general method for the 

 quantitative analysis of colouring matters, a method capable of surprising 

 refinement and accuracy, and which is based upon the relation which exists 

 between the extinction-coefficient and concentration, Vierordt has placed 

 both the sciences of physics and physiology under a lasting obligation. 2 

 To Hiifner belongs the merit of having developed and perfected the 

 methods of spectrophotometry, but especially of employing it so as to obtain 

 results of paramount importance to physiology, and which would have been 

 unattainable without its aid. Not only has he, by his own long-continued 

 researches, and those of his pupils, determined the spectrophotometric con- 

 stants of haemoglobin and its compounds with oxygen and carbonic oxide, 

 but he has by spectrophotometry succeeded in determining the absolute 

 and relative amounts of reduced and oxyhaemoglobiii existing side by side 

 in the blood. He has further shown that, as we now know the volume of 

 oxygen which can combine with 1 grm. of haemoglobin, by determining the 

 amount of haemoglobin and of oxyhsemoglobin coexisting in any specimen of 

 blood, we possess data enabling us to calculate the volume of the dissociable 

 or respiratory oxygen of the blood, without having recourse to direct deter- 

 minations by means of the mercurial pump and gas analysis. 



Further, by the method of spectrophotometry, combined with the results 

 of chemical investigation, Hiifner has furnished us with the proof that, in 

 spite of the differences in many physical characters, and even in centesimal 

 composition presented by the blood-colouring matter of different animals, the 

 coloured iron-containing group existing in haemoglobin, upon which its essen- 

 tial physiological functions depend, is identical in all. 3 



General description of the visible spectrum of oxyhsemoglobin. 

 Instruments required. For the study of the visible, as distinguished from 

 the photographic spectrum of the blood, or of oxyhaemoglobin, the spectro- 

 scopes which are in common use in physical and chemical laboratories may be 

 employed, providing the dispersion of their prisms be not too great. A 

 spectroscope of the ordinary Bunsen type, provided with a single good flint- 

 glass prism, is infinitely to be preferred for the study of absorption spectra to 

 an instrument with two prisms, for, with the greater dispersion, absorption- 

 bands appear much less clearly defined than with the smaller. Direct vision 

 spectroscopes of the Browning or Hofmann patterns, or microspectroscopes, 

 i.e. direct vision spectroscopes adapted to the eyepiece of the compound 

 microscope, may be employed ; and the second class of these instruments 

 renders great services in the investigation of minute quantities of colouring 

 matters as, for instance, in the examination of the optical characters of 

 the colouring matters of the tissues. 



It is advisable, indeed for the purposes of original research indispensable, 

 that the spectroscope employed should furnish means of determining accur- 



1 Preyer's monograph, entitled "Die Blutkrystalle, " which appeared in Jena in 1871, 

 still continues indispensable to the physiological chemist. It is replete with original 

 observations of "great value, and establishes that Preyer had no unimportant share in the 

 development of our knowledge of the blood-colouring matter. 



2 Karl Vierordt, "Die Anwendung des Spektral-apparates zur Photometric der Absorp- 

 tionsspektren und zur quantitative!! chemischen Analyse," Tubingen, 1873; "Die 

 quantitative Spektralanalyse in ihrer Anwendung auf Physiologic, Physik, Chemie, und 

 Technologic," Tubingen, 1876. 



3 As the chief of Hiifner's papers have been already quoted, or will be referred to sub- 

 sequently in detail, their dates and titles are not given in this place. 



VOL. I. 14 



