HISTOLOGICAL CHANGES AFTER IRRADIATION 



1119 



ratus atrophies. This occurs in practically all mammals except the 

 mouse _i n which sterilization of all follicles in very young or adult mice 

 does not prevent later development of estrual cycles (Parkes, 1927). 



SKIN 



As might be expected from the different tissues that enter its structure, 

 the changes in the skin following irradiation vary considerably with the 



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Fig. 17-6. (A) Section through ear of mouse 24 hours after 5000 rep of external /3 rays. 

 The epidermis is of normal thickness, the derma is slightly edematous; 325 X. (B) 

 Lumbar skin 56 days after 12,000 rep of external /3 rays. The epidermis is greatly 

 thickened and the derma still shows some infiltration with inflammatory cells. This 

 thickening of the epithelium is typical of regeneration after severe injury to skin. 

 Hair follicles are absent, although there is a portion of the smooth muscle of a hair in 

 the lower left-hand part of the section; 210 X. (After Snider, 1948.) 



histological constitution of the several parts of the organ. One group of 

 changes occurs in the epidermis with its stratified squamous epithelium 

 and its derivatives, the hair and associated sebaceous glands, the sweat 

 glands, and the nails. In the other category of tissues are the vascular 

 connective tissues forming the derma and the subdermal tissues. The 

 smooth muscles of the hair may be included with this group. The 

 analysis of the changes in skin has been complicated by the long latent 

 period in the epidermis and by the fact that most of the human epidermis 

 is more sensitive and thicker than that of the laboratory mammals. This 

 probably explains its exceptional reaction to various chemical and 



