586 THE GASES OF THE BLOOD 



satisfactory mode, applicable also to estimation of the cir- 

 culating blood in the living human body. The subject in- 

 spires from a gasometer which contains a gas mixture of 

 known composition rich in nitrous oxide but providing suffi- 

 cient oxygen. The amount of nitrous oxide taken up by the 

 blood during respiration is determined by analysis. On the 

 basis of the determinations of Siebeck as to the intake of 

 nitrous oxide by blood it can then easily be determined 

 how much blood must have passed through the lungs to 

 have taken up at the given partial pressure the amount 

 removed from the mixture. 18 



Objective Hcemoglobinometry and Spectrophotomeiry. 

 Attention should be paid to two recent methods of interest- 

 ing device. In each the purpose attempted is an objective 

 hsemoglobinometry intended to make the observer independ- 

 ent of the question of keenness of his subjective sense- 

 perceptions. This is accomplished by J. Plesch by replacing 

 the eye of the observer in comparing the concentrations of 

 color solutions by a selenite cell traversed by an electric 

 current. It is well known that selenium possesses the prop- 

 erty of changing its electrical conductivity under the in- 

 fluences of light, apparently owing to a polymerization due 

 to the light. By having the light coming from a fixed source 

 traverse a trough filled with the color solution before falling 

 upon the selenium cell, the variation in current resistance, 

 which may be measured by a sensitive galvanometer, is 

 made to serve as an objective index of the degree of light 

 absorption. 19 



The other method referred to is a photographic record 

 of intensity dispersion in blood spectra recently perfected 

 by Wolfgang Heubner. 20 The method of spectrophotometric 



u J. Markoff, Franz Mttller and N. Zuntz, Zeitschr. f . Balneol., 4, Nos. 14- 

 15, 1911-12. 



M J. Plesch (N. Zuntz's Lab.), Biochem. Zeitschr., 1, 32, 1906. 



20 W. Heubner (Gottingen), VIII Intern. Physiologen-Kongr., Wien., Sept., 

 1910; Deutsche med. Wochenschr., 1911, No. 11; W. Heubner and H. Rosenberg, 

 Biochem. Zeitschr., 38, 345, 1911. 



