ORGAN AND BODY SYSTEMS 481 



information concerning the fundamental changes in tissues following 

 irradiation. The effects of radiations other than roentgen and gamma 

 rays could be studied to advantage by this procedure. 



BLOOD VESSELS AND THE RETICULO -ENDOTHELIAL SYSTEM 



It has already been mentioned that the erythema is a result of changes 

 produced by radiations in the capillaries of the skin. The endothelium 

 is damaged, as shown by a change in the permeability of the cells, and the 

 contractile power of the capillary muscles is altered (248, 284, 336). 

 Very little is known about the type of injury which may be produced, 

 aside from evidence obtained with the capillary microscope and from 

 cUnical observations. David and Gabriel (58, 60) first observed the 

 reaction of the blood vessels of the skin to roentgen rays of various wave- 

 lengths by means of this microscope. They found that long waves 

 produce a more vigorous reaction than short waves, a conclusion open 

 to some doubt because of their uncertain dosage. The reaction appears 

 first and is most striking in the superficial layers, and the capillary 

 network stands out in a strongly reddened background. With the 

 shorter wave-lengths the damage appears later and later. Dilation 

 of the capillaries is the most characteristic change. Some observers, 

 however, have reported an initial constriction (192). These observations 

 should be repeated with calibrated wave-lengths and accurately meas- 

 ured doses. The tonus of the capillaries may be altered in other organs 

 (111). Turano (355) points out that the damage occurs before histo- 

 logical changes can be seen. He believes that the capillaries in patients 

 with vasodilation, due to disease or imbalance, are more sensitive to both 

 ultra-violet and roentgen rays than are normal vessels. The dilation 

 may continue for as long as two months (192). The endothelial cells 

 show granules with vital stains after irradiation (288). 



Histological studies of blood vessels in fixed tissues show only late 

 changes (184, 282, 284, 309). The more acute changes are probably 

 in the realm of functional response to local damage of the endothelium 

 or to the mechanism controlling the size of the capillary itself. That is, it 

 may be either direct or indirect. Zwerg (403, 404) found no change in 

 the blood vessels or in the muscles with doses as high as 5600 to 9600 r, 

 given by the fractional method. 



The effects of both ultra-violet and roentgen radiations on the reticulo- 

 histiocytic system have been studied by Castellino (40) who observed 

 that in guinea pigs, vitally stained with trypan blue, the number of 

 histiocytes was increased. The cells were full of granules. Occasional 

 Langhans cells and some fibroblasts stained blue. Similar observations 

 have been made on mice and rats (244, 288). These reactions he con- 

 sidered to be evidence of a stimulation of this system. Phagocytosis 

 may be increased by moderate dosages of roentgen rays (18, 286). 



