the Optical Rotation of the Proteins of Blood Sera. 193 



Section j3 has been developed in only a few cases. The most notable 

 observation is that the absorption in this region is usually very small. The 

 curves and especially the spectrum photographs demonstrate in several cases 

 that the maximum extinction coefficient is considerably less than O'Ol. It is 

 certainly very much less with the proteins than it is with serum. 



Section <y presents no peculiarities, save only that the sweep is broken by 

 four or five " steps," especially by a prominent one not far from extinction 

 coefficient 0'25. 



Section 8 is found to characterise all the proteins more or less, although not 

 always in so pronounced a manner as many sera. The mean curve does not 

 exhibit this quite so well as the individual curves do, as the construction of 

 the mean curve has a smoothing-out effect. With human eu-globulin, the 

 head of the curve is narrowed from both sides. 



' Section e is usually the most irregular in form for any given specimen, and 

 it is here that there is most disturbance in the wave-length. This is partly, 

 but not wholly, accounted for by the " steps." 



Section £ defines the limit of the general absorption, and shows very little 

 variation. Only slight " steps " occur occasionally. The most notable feature 

 is that it bends sharply towards the red at the bottom where it joins the 

 Section e. 



Summary. 



1. The primary object of the investigation was to ascertain the contribution 

 made by each protein constituent of serum to the ultra-violet absorption 

 spectrum curve of blood serum. 



2. It has been shown that the absorption curve of pseudo-globulin is 

 constant, and is the same for both the horse and human varieties. 



3. The absorption curve for eu-globulin differs considerably from that for 

 pseudo-globulin in extinction coefficients, but not in general form. This 

 favours the view that the differences between pseudo-globulin and eu-globulin 

 do not result from differences in the structure of the chemical molecule. 



4. The absoption curves for the horse and human varieties of albumin have 

 been shown to be the same, except for a constant ratio in their magnitudes, 

 and this difference may be due to the physical, or possibly chemical, associa- 

 tion of an aggregate, possessing little or no selective absorptive power — for 

 example, an aliphatic amino-acid or a polypeptide — with the principal or 

 absorbing aggregate. 



5. The close similarity in form of all the curves when corrected to a common 

 amplitude and the fact that the amplitudes are nearly all simple multiples of 

 a common factor, point to similarity of constitution amongst these proteins 

 and to a variable " concentration" of the active group. 



