DAVID L. DRABKIN 



in the different species to their body mass. The quantity of cytochrome 

 c on the other hand, in rat, man and cow, was proportional to a 

 fractional exponent of their body weight, or, if you prefer to express 

 it that way, to their surface area. The total cytochrome c of the horse 

 (Table III) does not fit this relationship for reasons which need not be 

 discussed here, but it may be seriously suggested that this discrepancy 

 has something to do with the difference expressed by the phrases 

 • excitable horse ' and ' placid cow '. 



Variable Aperture, Set to Match 

 Extinction at Wavelength of 

 Minimal Absorption 



Longitudinal Section Through 

 Cuvette of Capillary Bore 



(Drawn to Scale) 



Figure 6. An exact diagrammatic representation of the align- 

 ment of the photometer, capillary cuvette, and iris diaphragm 

 in the micro spectrophotometric determination of cytochrome 

 c in tissues {Rosenthal and Drabkin 9 ). 



48 



