190 Dr. S. J. Lewis. Ultra-Violet Absorption Spectra and 



extinction coefficient of the head of the band against 2420 for any of the 

 globulins, and to this one may perhaps attribute the higher figure, 2543, for 

 the wave-length of the foot of the curve in the albumins. The inference 

 from this is that the general absorption of the simpler body in albumin is 

 somewhat greater than it is in the globulins. It is interesting also to observe 

 that the absorption curve of pseudo-globulin which has the greatest amplitude 

 proved to be the most constant of all in the course of the experiments now 

 described, and was the same whether for horse or man, and would thus appear 

 to be a much more definite substance than either en-globulin or albumin ; it 

 may even be a chemical entity. 



On the other hand, it is possible that the differences between the absorption 

 spectra of the proteins are essentially chemical in their significance, and then 

 they are not capable of such simple explanation. 



The Absorption Curves. 



It will be seen that at the foot of each column in the Tables I to VI, an 

 " adopted " value is given. - This value is not the arithmetic mean of the 

 experimental figures, but the value deemed to be the best after considering all 

 the circumstances, giving great weight to the most successful experiments and 

 little or nothing to those of doubtful value. Hence, the factors for the later 

 and better specimens differ only very slightly from the adopted values as 

 shown in the Tables. 



With these values a mean curve has been drawn in the following way. 

 First, the band for each separate specimen of protein, that is the part of the 

 curve covered by the " difference " or " amplitude " values was divided at the 

 proper extinction coefficients into ten equal parts and the points of division were 

 designated " position " at the extinction coefficient of the head, " 1st position" 

 one-tenth of the way down, " 2nd position " two-tenths of the way down, and 

 so on until the " 10th position " is at the extinction coefficient at the foot of 

 the depression. All the curves were then re-drawn to the scale expressed by 

 the adopted amplitude or " difference " of extinction coefficient. 



'Next, the wave-length at each " position " on the curve was read from the 

 curve for each specimen, and a value adopted. The adopted values are set 

 out in Table VIII and have been used in plotting the curves (see p. 192). 



It should be observed that although the mean curves show points plotted 

 at only about twelve extinction coefficients, and at similar positions for all the 

 specimens, absorption spectra were photographed at 50 or more extinction 

 coefficients, and hence each original curve has a corresponding number of 

 points plotted, similar to those plotted in the curve figured in the first paper. 



