VISIBLE Si'l'A TRUM OF OX )//. EMOGLOBIN. 209 
many persons of distinction in all countries, amongsl the first and most 
successful of whom were W. Preyer ] in Germany, and Sorby and Ray 
Lankester in England. Amongsl 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 Biifner. 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 spectrophotometry con- 
stants of luenioglobin and its compounds with oxygen and carbonic oxide, 
but he has by spectrophotometry succeeded in determining the absolute 
and relative amounts of reduced and oxyhemoglobin 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 oxyhemoglobin 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. 
— Instrument* required. — For the study of the visible, as distinguished from 
the photographic spectrum of the blood, or of oxyhemoglobin, 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 (dearly 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. 
- Karl Vierordt, "Die Amvendung des Spektral-apparates zur Photometric der Absorp- 
tionsspektren und zur quantitativen chernischen Analyse," Tubingen. 1873; "Die 
quantitative Spektralanalyse in ihrer Amvendung auf Pbysiologie, Physik. Chenrie, und 
Technologie," Tubingen, 1876. 
s As the chief of Hufners 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 
