442 RADIATION INJURY AND LETHALITY 



we can say that essentially nothing we do is without hazard and that life 

 is a succession of naive and qualitative risk calculations, it is in radio- 

 biology that man has elected to attack such a problem squarely and is 

 finding it necessary to evolve and put under scrutiny some new or neg- 

 lected concepts. Whether this has had an irrational or a rational origin 

 is beside the point; if one is willing to be more inquisitive than irritable 

 it is bound to become scientifically fruitful. 



Let us follow the development of mammalian radiobiology from the 

 purely descriptive phase, through that of quantitative physiology, and 

 into the beginning of the theoretical phase just mentioned. We will 

 limit ourselves, for the most part, to the effects of penetrating total- 

 body irradiation, understanding that partial-body effects can often be 

 deduced therefrom. Studies of partial-body responses by experimental 

 techniques are, of course, of great importance in elucidating the total 

 physiological picture. A case in point is the remarkable series of findings 

 of Jacobson and associates where a very large part of the body (all but 

 the spleen) has been irradiated (1). In certain cases paradoxical findings 

 of the greatest potential significance have turned up. As examples of 

 the latter we can mention the epilation of a non-irradiated parabiotic 

 partner (2) and the ineffectiveness of partial-body irradiation in the in- 

 duction of mouse lymphoma (3). 



The initial radiation response, or the radiation sickness of radiologi- 

 cal practice, is known as a benign but unpleasant state occurring during 

 the first few hours following irradiation, and such evidence as is avail- 

 able suggests that the autonomic nervous system plays an important 

 role in this syndrome. Certain animals (rabbits and birds) may suc- 

 cumb during this initial period without the overwhelming dosage (100 

 times the LD^q) necessary to cause immediate death in most species (4, 

 5). The occurrence of immediate death in the chick has been shown to 

 be remarkably dependent upon dosage rate (6) and is associated with 

 rapid accumulation of uric acid in blood and tissues (7), which may ac- 

 count for the special susceptibility of birds to early death. In the rabbit, 

 hypotension is characteristically seen after total-body irradiation (8). It 

 may be that the well-known lability of its peripheral circulation lies be- 

 hind the early susceptibility of the rabbit. 



One of the most remarkable things about irradiation death in the 

 higher animals is the length of time between the physicochemical events 

 which must be primarily responsible for death and the appearance of 

 symptoms. Another is the relatively very large dosage necessary to kill 

 most animals (with the exceptions noted) in a short period, dosages 

 which are comparable to those which denature proteins. Thus the bulk 

 of the pathological effects are ''secondary," at least in time. 



