930 BIOLOGICAL EFFECTS OF RADIATION 



after exposure, the bacteria are plated in Wright cells. The method of 

 Wolff and Ras appears at first sight very simple, but if we consider 

 that the method involves the removal and handling of only 2.5 mm.' of 

 suspension, it would seem, at least, that extensive experience would 

 be necessary to handle these small quantities, so that each 2.5 mm.' should 

 contain the standard number of bacteria. The difficulty of handling 

 such small quantities of material is probably the reason why this method 

 has not become more popular. 



BIOLOGICAL MATERLALS AND EXPERIMENTAL CONDITIONS 



Besides yeast, bacteria, and onion-root tips, a number of other 

 detectors have been used. There is a group of articles (77, 81, 182 to 184) 

 describing the use of sea-urchin eggs as indicators of the production of 

 mitogenetic rays. Apparently good effects have been obtained, but 

 since sea-urchin eggs are not available the year round and since the 

 laboratories where sea-urchin eggs can be had are few, this method has 

 not been used extensively. Positive results have also been reported 

 with fungus spores (248), speed of enzymatic reactions (190), and the 

 increase in number of mitotic figures in certain tissues of the eye 

 of rabbits (exposed contrasted with nonexposed) (117). 



In 1930 Stempell published several articles (275 to 286) on the 

 detection of mitogenetic rays by their effect on the formation of Liesegang 

 rings in gelatin, etc. He obtained the effect through cellophane. That 

 the action on the rings was mainly a chemical one, caused by the vapors 

 given up by the supposed mitogenetic-ray sender was shown by Tokin 

 (291), Siebert (265), and others. Later Stempell and Romberg (279) 

 reported this fact themselves. However, in an extensive publication 

 the same authors (283) give some experiments as a result of which 

 they believe that they have obtained some effects through quartz. The 

 use of Liesegang rings as a detector has not since been reported. 



In all the work with biological detectors certain very definite features 

 should be emphasized. All the biological materials, especially the 

 microorganisms, should be used as detectors when not in a state of most 

 rapid multiplication. It has been indicated previously that the yeast 

 should be in the "lag" stage (cf. Tuthill and Rahn, 292). The view 

 held is that when in a rapid state of development no additional growth 

 can be expected with the food materials available. Moreover, all 

 conditions should be as standardized as possible. The dilution of the 

 organism in suspension and the type of nutrient solution should be 

 adjusted to the special strain one uses. 



Certain questions are suggested. Are the detectors quantitative 

 indicators? Do they show great response to increased intensity? In 

 both cases the answer is in the negative. They will respond within 

 certain limits, that is, they may respond quicker to a so-called intense 



