REACTIONS OF NERVES AND MUSCLES TO RADIATION 



295 



Fig. 7. — Leech muscle rinsed with Ringer solution at pH 8,0, aerated with O2 only. Re- 

 peated irradiation with a dose-rate of 10,000 r/niin and irradiation times (from left to 



right) of 10, 20, 25 and 30 sec. 



time, i.e. the dose. Shortly after irradiation the relaxation becomes 

 apparent and seems to follow an approximately exponential curve. 

 Repetition of the irradiation and thus increasing the accumulated total 

 dose results in a residual contraction which becomes more and more 

 prominent. The rate of relaxation diminishes with the accumulated 

 dose. 



If such a normal muscle is irradiated continuously with suitably 

 chosen dose-rates a kind of steady state of contraction is produced 

 (Fig. 6). If, during irradiation with a certain dose-rate, no further con- 

 traction occurs, then irradiation with a higher dose-rate induces an 

 additional shortening of the same preparation until a higher degree of 

 final contraction is reached (Fig. 8). 



Fig. 8. — Leech muscle (rinsed with Ringer solution at pH 8.0; O2 saturated). Consecutive 

 irradiation with two different dose-rates. Lender irradiation with a dose-rate of 594 r/min 

 for 77 min a steady state of contraction is reached. After irradiation ceases the muscle 

 relaxes. The following irradiation with a dose-rate of 4,000 r/min produces a steeper 

 contraction curve and a higher final contraction. See also the difference in latency time. 

 f start and J end of irradiation. Time marks: 30 sec. 



DISCUSSION 



The radiation-induced contraction seems to be a complex process in 

 which at least two components may be distinguished: namely an 

 immediate contraction, which is reversible if the metabolic processes 



