ORGAN AND BODY SYSTEMS 521 



very sensitive tissues should be placed above or below the well known 

 sensitivity of the lymphocyte and the lymphoid structures including the 

 spleen, in evaluating their relative position in the scale. The gonadal 

 cells, especially the immature forms, are quite sensitive to roentgen irradi- 

 ation but less so than those tissues just mentioned. In a descending 

 scale of sensitivity, beginning with a moderate sensitivity, we may list 

 certain tissues in the following rough order: the thymus, the stomach, 

 colon, and bladder epithelium; salivary epithelium, probably kidney 

 epithelium, hair papillae, blood-vessel endothelium, fibroblasts, and 

 young connective-tissue cells including collagenous fibrils. Next in order 

 of sensitivity are: the mucosa of the mouth, esophagus, rectum, and 

 vagina, the lung parenchyma, pleura, skin epithelium, and the struc- 

 tures of the eye. The liver and adrenal (cortex more than medulla) 

 are thought by some to be relatively sensitive but to possess tremendous 

 regenerative power — which obscures evidence of damage. This needs 

 clarification. Next come the smooth, striated, and cardiac musculatures, 

 cartilage, bone including osteoblasts, teeth, normoblasts, Sertoli's cells, 

 and stroma cells of testes and ovary. There is some doubt concerning 

 the relative sensitivity of the pancreas. The most resistant cells may be 

 listed in the followdng order: adult thyroid and parathyroid (?), adult 

 pituitary, brain and nerve cells, nerve trunks and endings, tendons and 

 joint capsules, i.e., adult speciahzed connective-tissue structures, adult 

 sperm cells, and red blood cells. The red blood cells and adult sperm cells 

 have resisted the highest dosage administered to body tissues. 



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