426 PHYSIOLOGICAL FACTORS IN MAMMALS 



Jones : 



Our experiments indicate that an indirect effect on desoxyribonucleic acid 

 metabolism is seen. We agree with Hevesy's experiments on the linearity of 

 response in depression of desoxyribonucleic acid metabolism with doses up to 

 300 r. 



Kohn: 



In connection with the so-called "indirect effects" of irradiation upon cell 

 division, it is of interest to recall an experiment by Friedenwald published some 

 years ago, in which it was shown that the mitotic index of the cornea (mitotic 

 figures per unit area) fell from about 100 to almost zero during the hour following 

 excitement of the animals. This effect could be blocked by atropine (paren- 

 terally), and could be mimicked by instiUing epinephrine into the conjunctival 

 sac. Direct irradiation of the cornea, of course, can produce a similar fall in 

 mitotic index. This example is not an isolated one, and it seems that many of the 

 effects observed in radiation experiments have pertinent parallels elsewhere, 

 both with regard to the setting up of controls and to general interpretation. 

 It seems to me that very few of these have been considered during the course of 

 these meetings. 



Edelman : 



1. In regard to Smith's remarks [see discussion following paper by Evans, 

 p. 411] about the LD^, may I state that the LDeo in our laboratory has risen in 

 3 years from 650 to 850 r. Critical examination of the records makes it appear 

 that the shift in the lethal-dose values is due to better facilities for survival in 

 handling and care of the animals. The LD50 is variable, and suitable controls 

 must be run with each experiment. 



2. I also want to echo Kohn's sentiments about the exciting of animals. Rats 

 placed in a tight cage and x-rayed show an 80-90 per cent drop in leukocyte 

 count 3 hr after 600 r. Controls, similarly restrained and placed under the 

 machine with the tube on but with the lead cover in place so that the animal 

 receives no radiation, show a leukocyte count drop of 70-80 per cent. This is 

 transient, the count returning to normal after several hours, but these facts must 

 be known and taken into consideration in radiation work. 



3. Margaret Holt, in our laboratory, could not observe any bilobed white 

 cells in smears made at intervals for 96 hr after exposure to 600 r of x-radiation. 

 This, however, may be due to their infrequent occurrence and to the few (100- 

 150) cells counted per animal. 



