328 RECOVERY FROM FLUORITE RAYS 



isms in the class requiring 10 seconds as there are in the classes re- 

 quiring 12 or 14 seconds exposure to produce cytolysis. The point 

 at 8 seconds is the only one which does not fall upon the straight 

 line and this point could be brought very close to the line by omitting 

 the results of the experiments of 1 day in which the death rate was 

 abnormally high. Such a distribution of susceptibility will have no 

 effect upon the shape of the recovery curve, and we may conclude 

 that the correspondence of the recovery rate with an exponential 

 function of time is not entirely accidental but is the result of an orderly 

 occurrence of the processes involved in the recovery from fluorite 

 radiation. 



We may find a cause for such uniformity if we assume that cytol- 

 ysis occurs when a certain amount of some toxic photoproduct has 

 been formed. (The fact that no cytolysis occurs until the length 

 of exposure is increased to 6 seconds is in harmony with such an 

 assumption.) Recovery then, depends upon the removal of the toxic 

 substance. This removal is accomplished by orderly processes. 



Since the rate of recovery is so nearly represented by the mono- 

 molecular reaction formula, processes of a chemical nature suggest 

 themselves. Other processes, however, may be conceived. If for 

 example, the toxic substance were removed by diffusion out of the 

 organism, the rate of recovery might correspond very closely to an 

 exponential function of time, especially if the rate of diffusion in the 

 outer limiting membrane were slow as compared with the rate within 

 the cytoplasm. For in this case, since the concentration outside of 

 the organism would, due to the ciliary action, always be zero, the 

 amount of toxic substance diffusing across the membrane in a given 

 time would be proportional to the concentration of the toxic substance 

 remaining within. 



Wood and Prime^ advanced a similar explanation for their observa- 

 tion that it required a much longer exposure to kill carcinoma tissues 

 in vivo than in vitro. They say^: "The constant supply of fresh nutri- 

 ment to the cells by the blood and the removal of any chemical prod- 

 ucts formed by the radium in the tissue, must account for this dif- 



^ Wood, F. C, and Prime, F., Jr., The action of radium on transplanted 

 tumors of animals, Ann. Surgery, 1915, Ixii, 751. 

 ^ Wood and Prime, Ann. Surgery, 1915, Ixii, 759. 



