ORGAN AND BODY SYSTEMS 477 



very low intensity radiation over a very long period of time. The last 

 usually concerns small amounts of radium or radium emanation. Most 

 of the experimental work done upon animal tissues up to a recent date 

 has been done with the massive-dosage method, so that the physiological 

 effects presented concern chiefly this type of dosage, but of recent years 

 the other methods have been employed to a considerable extent, though 

 as a rule for therapeutic purposes only. Experimental observations made 

 upon the skin of patients jdeld information of value in depicting the 

 changes which may occur under these variations of dosage procedure. 



SKIN 



Although the effect of radiations on the skin has long been studied, 

 the sequence of the changes which follow exposure and the explanation 

 of such changes are not fully known. The reaction involves the epithe- 

 lium, the blood and lymph vessels, connective tissue, and other struc- 

 tures which contribute to the nutrition and support of the epithelium. 

 The amount of reaction to a definite dose seems to vary with the thickness 

 and location of the skin (169). The epilation dose and the erythema 

 dose for animals are almost 4 times as great as for the human skin. 



The histological changes have been extensively studied (9, 183, 276). 

 Rost (305) describes in detail the effects of massive irradiation with 

 roentgen rays. In the cutis there is an increase in connective tissue and 

 endothelial cells, a decrease and atrophy of elastic fibrils, with shrinkage 

 of the collagenous fibrils. Repair is slow and is accompanied by the 

 formation of atypical cells. Subsequently pigmentation occurs, involving 

 the disintegration of pigment cells. The pigment may be dispersed 

 into the surrounding structures and into lymph channels (223). Sweat 

 glands and the muscles of blood vessels show no change (154, 183, 213). 



Wolbach (393) has studied the changes which occur in human and 

 guinea pig skin after repeated irradiations which extended over long 

 periods of time. There is first a swelling of the subcutaneous collagen 

 bundles, a reaction which results in a greatly thickened corium. Coinci- 

 dent with this is a gross shrinkage of the skin and a destruction of some 

 connective tissue cells. Similar changes in the walls of blood vessels lead 

 to the ultimate occlusion of the latter. Subsequently the epidermal 

 cells swell and show abnormal mitoses (154). The maximum radiation 

 effect is on the superficial layer of the corium in which necrosis occurs. 

 Still later, the epidermis in the necrotic areas proliferates, while in the 

 corium there is a formation of new collagen bundles. In cases of chronic 

 roentgen ray dermatitis, normal collagen is replaced by dense, hyaline 

 collagen rich in elastic fibers (393). There is also obliterative thrombosis 

 in the blood vessels of the corium and subcutaneous tissues, and necrosis. 

 Representative proliferation of the epidermis then follows (25, 

 57, 61). 



