EFFECTS OF RADIUM RAYS ON PLANTS 989 



between minimum and optimum points, all metabolic activities, whether 

 constructive or destructive, are accelerated; but if the stimulus increases 

 from the optimum toward the maximum point it becomes an over- 

 stimulus, and all metabolic activities are depressed and finally completely 

 inhibited. Beyond a certain point of overstimulus recovery is impossible, 

 and death results." 



A second broad generalization was also stated as follows: "If the 

 living matter itself is directly affected by the rays it is difficult to conceive 

 how any one function could be modified without the others being affected 

 for, with long periods of exposure ... to rays of high activity ... it is 

 certain that the protoplasm will have its vitality partially or wholly 

 destroyed,^ and all 'vital' processes correspondingly modified or stopped. 

 But, on the other hand, the modification or total inhibition of any one 

 process does not necessarily indicate that the living matter has been 

 directly affected, for such a condition would result, if, as in the case of 

 the resting seed, the rays destroyed an enzyme essential to the completion 

 of some function." 



Besides demonstrating that radium rays act as a true stimulus, the 

 work referred to served to suggest the direction that future investigations 

 should take. Of course, after anything has been found to act as a 

 stimulus, the effects of subjecting living organisms to it may be predicted 

 along broad lines (acceleration, retardation, inhibition of functions, or 

 killing the tissue or organism), but these effects need to be worked out in 

 detail, stated quantitatively, analyzed as to modus operandi, and practical 

 applications, if any, pointed out and tested. 



In a later paper Gager (26) reviewed the more important literature 

 that had appeared between 1908 and 1916. In a work appearing first 

 in 1915, revised in 1924, Colwell and Russ (17) devote two chapters to 

 plant material, but the survey is inadequate, and no attention is given 

 to American literature. Up to 1908 certain crudities were inevitable. 

 No precise quantitative method had been devised for expressing the 

 radioactive strength of radioactive compounds. There was no universally 

 recognized unit of radioactivity. Preparations of radium bromide in 

 sealed glass tubes were indicated as having various "activities," e.g., 

 10,000, 1,500,000, 1,800,000, meaning that the preparation was that 

 much stronger than an equal weight of uranium, for Eve had shown that 

 the activity of radium is a function of the amount present. Rutherford 

 had shown that the intensity of activity did not vary with the concentra- 

 tion of the salt. In his experiments, "a distribvition of radiating matter 

 over a thousand times its original volume has no appreciable influence on 

 its original activity." 



But there was no precise manner of designating the dosage at varying 

 distances of the active preparation from the plant, or of taking account 



1 This would have been differently worded at the present time. 



