488 BIOLOGICAL EFFECTS OF RADIATION 



Pf abler (266), using the theoretical concept of Kingery (176), has 

 undertaken to use the saturation method, which consists in applying an 

 erythema dose at high intensity within a short time in one sitting, and 

 then maintaining this effect over a period of time by means of "additional 

 smaller doses to correspond with the loss in effect during any given 

 period." The rate of loss is represented by a logarithmic curve. Accord- 

 ing to Stenstrom and Mattick (342), 50 per cent of the initial dose can 

 be added on the ninth day after a full erythema dose. But there is 

 some evidence that the interval depends on the wave-length of the radi- 

 ation employed (268). These additional doses cannot be given indefi- 

 nitely, but within certain limits the method gives increased destructive 

 effects on tumors. Reisner (293) is of the opinion that this method of 

 dosage is not so effective as Coutard's. 



The total amount of radiation which cells and tissues can tolerate 

 is very great. Chick embryo fibroblasts, exposed in vitro, will survive 

 doses of 6000 to 7000 r (163), while massive doses of 1200 to 1600 r upon 

 small areas (4 to 25 cm.-) of the human skin do not permanently injure 

 the tissues (24, 231). 



Pack and Quimby (258) believe, from their study of the skin erythema 

 produced by different intensities, that a greater amount of roentgen radi- 

 ation is required if the exposure is long. They point out, however, that 

 there must be a differential recovery of cells after the exposure to radi- 

 ation. A large number of experiments tend to support the theory that 

 normal cells recover much more quickly than do neoplastic cells. In a 

 review of the literature the authors find that there is a lack of agreement 

 regarding the influence of the intensity of the beam on the effect pro- 

 duced. Some investigators found that the reaction to a definite dose is 

 the same regardless of the intensity, while others believe that low inten- 

 sities are more effective. The majority claim that the reverse is true, 

 namely, that high intensities act most vigorously. Pack and Quimby 

 emphasize the work of Regaud (291) who showed that greater differ- 

 ential effects could be obtained on tumor cells than on normal tissues 

 with low intensity radiation. In their experiments on the production of 

 the erythema on the human skin they found that "if all the times used in 

 such an experiment are short in comparison with the duration of the 

 life span of the cell in question, no difference will be observed with differ- 

 ent intensities. If, on the other hand, the duration of exposure to radi- 

 ation of low intensity is comparable to the life span of the cell, 

 a different result may be expected, namely, that a greater effect is 

 produced on the skin by a stronger source acting for a short time than by 

 a weak source used for a correspondingly long time." (See 159, 161.) 



Holthusen (160) finds that the effectiveness of roentgen radiations 

 depends not on their wave-length but on the intensity of the beam. 

 Five hundred roentgens delivered at the rate of 500 r per min. produce the 



