S. C. BROOKS 177 



The average of the four values of the absorption coefficient is 110.2 

 and may properly be considered to be of the true order of magnitude. 

 This is about the absorption to be expected if light of a wave-length 

 of about 2530 Angstrom units were acting, while light of shorter 

 wave-lengths is much more strongly absorbed.^ The mercury arc 

 emits little light of wave-lengths intermediate between that of a 

 line at about 2530 Angstrom units and that of about 2930 Angstrom 

 units, and light of wave-length greater than about 2900 Angstrom 

 units has little or no effect on complement.'^ 



We may conclude that the principal effect of light on complement 

 is due to ultra-violet light having a wave-length of about 2530 Ang- 

 strom units; and that complement in layers of the depth used in the 

 experiments on the course of photoinactivation absorbs a large part 

 of the available light. For example, the most transparent sample, 

 having an absorption coefficient of 54.1, would absorb nearly 95 per 

 cent, the most opaque sample more than 99 per cent, of the incident 

 light of the effective wave-length. 



IV. 



It was necessary, as has been pointed out in the preceding section, 

 to determine whether or not there were changes in the transparency 

 of complement during the progress of photoinactivation. To settle 

 this point successive portions of complement were exposed for exactly 

 equal lengths of time in the inner of the two concentric quartz tubes 

 arranged as described above. In the space between the two tubes 

 was placed a portion of the same solution of complement; this portion 

 was left throughout the series of exposures. The total time of radi- 

 ation of this sample varied in different experiments between 18 and 

 25| minutes, and was long enough to reduce the efficiency of the com- 

 plement to less than that attained in any of the experiments on the 

 course of photoinactivation. Control experiments were conducted 

 which were similar except that the outer space was filled with distilled 

 water or with complement which had been completely inactivated 



^ Henri, V., Henri, Mme. V., and Wurmser, R., Compt. rend. Soc. bioL, 1912, 

 Ixxiii, 319. 



^Bovie, W. T., /. Med. Research, 1918, xxxviii, 335. 



