484 BIOLOGICAL EFFECTS OF RADIATION 



whole reaction lasts longer. The gamma-ray erythema has been studied 

 by Reisner (294, 297) who reviews the literature on this subject. He 

 finds that the doses previously given have been about 40 per cent too 

 high. Instead of 560 mg. el hr. at 1 cm. he believes that 310 to 330 mg. 

 el hr. (0.2 mm. Pt and 1.7 mm. brass filter) are adequate to produce 

 effects comparable to those which follow roentgen radiation. Braun, 

 however (29), finds no difference between the two when both are given 

 by the massive-dose method. 



The sequence of events following exposure of mouse tails to gamma 

 rays is essentially that found in the human skin, that is, erythema, 

 various degrees of epilation, desquamation, and ulceration (13). The 

 constriction, dry gangrene, and amputation of the tails were due to blood- 

 vessel thrombosis which is a late stage of severe injury. 



CONNECTIVE TISSUE 



The reactions of connective tissue to radiations have been mentioned 

 in the preceding sections (96, 369, 393). The behavior of individual 

 cells after exposure is best seen in tissue culture preparations (34, 52). 

 The latent period which occurs between the exposure and the first appear- 

 ance of injury has been studied by Fischer (102, 103) who used fibro- 

 blasts and osteoblasts from the embryo chick. He believes that the 

 length of this period is not dependent on the rate at which the cells are 

 dividing, and that it cannot be increased or diminished except to a small 

 degree. Contrary to the usual opinion, he holds that the absolute effect 

 of radiation is the same whether cells are dividing rapidly or slowly (102). 

 When very lightly irradiated cells are exposed to abnormal conditions, 

 such as high or low temperatures or poisons, which in themselves are not 

 injurious, the effect of the radiation is increased. This may be simply 

 an evidence of summation. 



The connective-tissue cells and the endothelium, together with the 

 blood-vessel-muscle cells which are relatively resistant to radiation 

 (163, 290) and the nerve endings and plexus in the capillary wall (whose 

 sensitivity is unknown) may all be involved in any changes brought 

 about in the various organs as well as in the skin by radiation. The 

 extent to which these tissues are involved is largely dependent upon the 

 dosage administered to the organ. The more resistant organs may show 

 injury only to the blood vessels while in other organs whose cells are more 

 sensitive, the capillaries play little part in the evident damage. This 

 indicates the great sensitivity of the cells in such organs. 



DOSAGE WAVE-LENGTH AND SKIN 



The relative effectiveness of different wave-lengths of radiation in 



producing the erythema reaction has been the subject of much research 



in recent years. The amount of energy required to bring about this 



response by means of heat is far greater than it is for ultra-violet, while 



