ORGAN AND BODY SYSTEMS 485 



the latter amount is greater than that needed to produce a roentgen-ray 

 erythema. Whether equal doses of roentgen rays, gamma rays, and 

 cathode rays are equally effective, is still debatable and must remain so 

 until the intensity of these radiations can be measured in equivalent units. 

 Stahel (339) compared the activity of roentgen and gamma rays on the 

 basis of erg/cm.^ absorbed, and found that while the roentgen-ray ery- 

 thema dose (600 r) is equal to 96,000 erg/cm.-, the gamma-ray dose may 

 rise as high as 8,000,000 erg/cm.- Such estimates are very questionable. 

 Although roentgen rays can now be measured accurately in terms of 

 roentgens, the question is not yet settled whether all wave-lengths are 

 equally effective (75, 76). Many observers (14, 15, 42, 77, 122, 151, 

 153, 199, 252, 270) believe that when the areas exposed are equal, as well 

 as the intensities of the beams, and the doses, measured in roentgens, 

 the erythema reaction is the same for all ordinary wave-lengths. Others, 

 however, maintain that the soft rays act more vigorously (7, 97, 106, 118, 

 121, 225, 226, 311, 327). A summary of some of the opinions on this 

 point is given in the table. Glocker (123) and Pohle (281) present evi- 

 dence to show that when a full erythema dose of 700 r is given, the skin 

 reaction is the same for all qualities of roentgen rays within the region 

 which they explored. But softer rays appear to be more effective w'hen 

 given in small doses. Reisner and Neef (297) have made a careful study 

 of this problem, using accurately measured doses. They conclude that 

 when the area exposed is small (4 cm.^), the reaction to equal doses of 



o 



roentgen radiation having wave-lengths from 0.14 to 0.26 A are equal. 

 Softer rays are more effective. With a larger area (50 cm.-) the range 

 of wave-lengths within which an equality of effect occurs is somewhat 

 greater. 



Still another view is that the effectiveness steadily increases with 

 increasing wave-length from a minimum to about 0.45 A (311). From 

 this point onward it decreases (118, 327). According to Meyer and 

 Glasser (225) the number of roentgens required to produce an erythema 

 by means of different roentgen ray wave-lengths, divided by the half- 

 value layer in water of those beams, is practically a constant. 



In recent years the method of dividing the total dose into fractions 

 which are given at frequent intervals over a period of days or weeks has 

 been widely used (cf. 242). Reisner (295) compared the effect of such 

 doses with that of a single massive dose. The latter, a "tolerance dose" 

 was 1100 r on a field 2 by 2 cm. Using this as a standard, he found that 

 equal skin reactions could be obtained by giving 27 daily exposures, each 

 of 10 per cent (llOr); or 7 exposures of 30 per cent each. For a full dis- 

 cussion of the effects of these and other arrangements of divided doses 

 the original paper should be consulted. In each case, when doses are 

 small and are given over an extended period, the tolerance dose, meas- 

 ured in roentgens, is greatly increased. 



