ORGAN AND BODY SYSTEMS 489 



same effect as 1000 r delivered at the rate of 15 r per min. Equivalent 

 amounts of radium or roentgen radiations have equivalent effects on the 

 skin, if the intensities of both are the same. This conclusion is in agree- 

 ment with that of Quimby and Pack (286), although other work (97, 287) 

 seems to indicate that there may be some difference in the effectiveness 

 of different wave-lengths. Holthusen's suggestion, that radium may 

 produce a stronger reaction in the second wave, may be but a variation 

 which has been pointed out by Miescher (227) of identical doses, or it 

 may explain why it is possible to give a slightly greater total dosage of 

 roentgen-ray and gamma radiation combined than of either alone (286). 



Experiments to test this latter point indicate that when roentgen 

 rays, gamma rays, or ultra-violet, in various combinations, are used 

 to produce an erythema, about one-third more radiation must be admin- 

 istered than when any one of these agents is used alone. This appears 

 to be true for combinations of gamma rays and hard beta rays, gamma 

 rays and hard roentgen rays. With equal parts of ultra-violet and soft 

 roentgen rays, the erythema is not produced even after a 50-per-cent 

 increase in the dose (108, 280, 285, 287). 



The intensity of radiation, which is an important factor in determin- 

 ing the amount of reaction of the skin to equal doses, seems to play no 

 part in the response of some other tissues (14, 15). Mouse tails exposed 

 to equal doses of widely different intensities of beta and gamma rays 

 respond equally. Bagg and Halter (15) have used this method to com- 

 pare the relative effectiveness of roentgen and gamma rays. When very 

 small areas are exposed, the effect of 400 mc. hr. is the same as that of 

 2350 r. The filtration of the radon was by 2 mm. brass and 3 mm. bakelite. 

 Experiments with the rabbit's ear showed that for a larger area (28 cm. 2) 

 the emission from 1 gm. of radium at 1 cm. distance is approximately 

 equivalent to 100 r per min. 



Failla (97) in reviewing the effects of various wave-lengths produced 

 by 200 and 700-kv. roentgen rays, and gamma rays, believes that there 

 is a true differential action of radiation for human skin as compared to 

 other test objects, and that 700-kv, radiation is intermediate in its effects 

 between the 200-kv. radiation and gamma rays. 



Grenz rays are absorbed almost completely (88 per cent Ijy 3 mm. of 

 human skin) in the surface, while roentgen and gamma radiation are 

 mostly transmitted by the skin (31). While measurements of quantity 

 are not yet established, it is thought that 250 r produces an immediate 

 mild erythema (119, 295). Reisner (295) found that doubling the dose 

 (4-cm.^ field) gave increasingly severe reactions up to 4800 r. The 

 reaction from 2400 r of Grenz rays was equivalent to that produced by 

 1000 r of 200-kv. roentgen rays. 



It is the reviewer's opinion that clinical experience and animal experi- 

 ments seem to bear out the fact that there is some difference in effect 



