158 



BIOPHYSICALLY ACTIVE LIGHT 



used. Examples of such scales used in clinical work are shown in Fig. 

 IV-17. 



Photronic Cell Colorimeters 



A photronic cell colorimeter of very simple design as suggested by- 

 Evelyn [1936] is shown in Fig. IV-18. 



Since the light transmitted by the absorption cells is a logarithmic 

 function of the concentration, one may obtain linear readings by using a 



circuit which reacts with a loga- 

 rithmic response to the transmitted 

 light. A device of this kind is the 

 logarithmic response vacuum-tube 

 voltmeter used by Muller and Kin- 

 ney [1925] in their design of a 

 photoelectric colorimeter. 



Absorption of Ultraviolet 

 diation by Proteins 



Ra- 



Fig. IV-18. Colorimeter design after 

 Evelyn [1936] showing use of a pho- 

 tronic cell. Source of light L, with 

 reflector, produces near parallel beam 

 through filter F. Light beam limited 

 by external stops in opaque cover over 

 a 6-cc parallel fused absorption cell C. 

 Energy incident on photronic cell (PC) 

 directly connected to microammeter, 

 of less than 50 ohms resistance, which 

 reads current developed by PC. 



The absorption of ultraviolet ra- 

 diation by serum proteins was inves- 

 tigated as early as 1922 by Judd 

 Lewis. Improvements in design of 

 the rotating sector quartz spectro- 

 photometer made it possible for F. C. 

 Smith [1929] to obtain the absorp- 

 tion spectrum of horse and human 

 serum proteins with a great de- 

 gree of precision. These results are 

 shown in Fig. IV-8. It will be noticed that as the wavelength decreases 



o o 



from 3000 A to 2790 A the extinction coefficient rises very rapidly, 

 indicating the approach to a sharp opacity at 2790 A. Then, with 

 decreasing wavelength, the material becomes more transparent, and 



o 



reaches a relatively high transparency at 2500 A, from which minimum 



o 



it rises very rapidly to high absorption values at 2000 A. These graphs 

 indicate that the absorption spectra of these proteins are the same, 



o 



except that the extinction coefficient for globulin at 2790 A is nearly 

 double that of albumin. 



It is possible by means of such absorption measurements to determine 

 the ratio of albumin to globulin in small amounts of cerebrospinal fluid. 

 This type of curve may also be used to indicate the purity of a given 



o 



sample of protein by comparing the values obtained for k at 2790 A 

 with those at 2500 A. 



