ORGAN AND BODY SYSTEMS 503 



appearance throughout, the cross striations are less clear and distinct 

 than in normal tissue, and the staining properties of both protoplasm 

 and muscles are poor. Fibrosis is frequent, and peculiar in that it is 

 diffuse and in fine strands between the individual muscle fibers. In 

 addition, there is a large amount of loose areolar tissue present and the 

 tissues are edematous. In further experiments on rats (380) the precor- 

 dium was exposed to beams of two different wave-lengths (0.19 and 

 0.34 A). The doses varied from 500 to 1000 r. No clinical symptoms 

 could be observed which might indicate a heart injury. The only gross 

 pathological change consisted of a dilatation of the right ventricle. 

 Microscopically, Zenker's necrosis in various degrees could be demon- 

 strated, and an increase in stroma nuclei with small foci of lymphocytes. 

 From these results it appears that the tolerance dose for the myocardium 

 of adult rats is about 500 r, effective in the heart. Werthmann (385) 

 exposed rabbits to repeated doses of 500 r each. The total dose varied 

 from 8500 to 21,500 r, the exposures extending over long periods. He 

 reports an atrophy of the muscle fibers with fracturing, empty sar- 

 colemma cells, simple nuclear degeneration, and changes in the connective 

 tissue with perivascular fibrosis and sclerosis. The sarcoplasm may 

 show some coagulation and necrosis (99). Dilation of the heart to two 

 or three times its normal size was found by Hartmann (136). It was 

 confined for the most part to the right auricle and right ventricle, the 

 former being hemorrhagic and its muscle replaced by areas of hyaline 

 degeneration. This did not occur in the ventricular walls. 



The effects of radiations on the conductive system of the sheep heart 

 have been studied by Hartmann (136). "Microscopically, the larger 

 and smaller branches of the auriculoventricular bundle are well preserved 

 when compared with the damage to the muscle proper. The larger 

 branches showed only thinning of the fibrils at the margin of the cells 

 with vacuolation and distortion of the nuclei, while some of the smaller 

 branches which lie in areas where the muscle stains poorly and is infiltrated 

 by leucocytes, show individual cells distorted, vacuolated, poorly stained, 

 and with shriveled nuclei. The infiltration, however, does not extend 

 into the branches of the bundle and in no case was hemorrhage or com- 

 plete destruction of the bundle found." 



When the muscle power of the heart is weakened either through 

 changes in blood supply or direct damage of the muscle cells or conduction 

 system, the changes in any of the hydrodynamics of the pulmonary 

 circulation elsewhere might well be reflected in extensive cardiac dys- 

 function. Any disturbance of the conduction system would probably 

 upset the rhythm, in certain cases at least. The electrocardiographic 

 changes may be explained by changes in the conduction system or shifts 

 in the shape of the heart, due to dilation, hemorrhage into the muscle, 

 etc. Such changes are only produced with high dosage. 



