924 BIOLOGICAL EFFECTS OF RADIATION 



There are two serious objections which have been raised to the onion- 

 root technique: (a) The mitotic figures are naturally not uniform in a 

 cross section of the root, that is, mitotic figures are usually more numerous 

 on one side than on the other, growth being somewhat rhythmically 

 progressive. (6) It is possible to produce changes through pressure, 

 uneven moistening, and other factors scarcely controllable, and these 

 may in themselves induce a considerable preponderance of mitotic 

 figures on one or the other side of the root. 



Objections to the work on the two bases mentioned above are reported 

 in a number of papers and extensive experimental evidence is given to 

 sustain these objections. The second point especially has been the 

 center of the attack on the Gurwitsch method. To mention only a few 

 of the investigators who have been unable to repeat Gurwitsch's work on 

 the onion root, I should at least refer to the following: Moissejewa 

 (200 to 202), Rossmann (234), Taylor and Harvey (290), and Wagner 

 (303). Gurwitsch has not used the onion root as detector now for several 

 years but has replaced this method with a yeast technique — a technique 

 which appears at first to be simpler and more easily controlled. 



YEAST AS DETECTORS OF MITOGENETIC RADIATION 



The yeast method was first described by Baron (12) m Gurwitsch's 

 laboratory. It has been modified and extended by many investigators, 

 although all of these use about the same general type of procedure, 

 varying the details slightly. Nevertheless, no complete description of 

 the technique has been published and the account by Baron (103) in 

 Abderhalden's "Handbuch" is not up to date, since the method has been 

 revised in many particulars. 



The reported advantages of the yeast method are that this organism 

 is composed of fairly large cells easy to count, that the method can be 

 standardized, and that pure cultures are readily maintained. To be 

 able to use any yeast technique successfully (that is, in obtaining positive 

 results) one must first have acquired, it is said, some facility in handling 

 this material. Still, each investigator in any other laboratory must work 

 out his own special procedure. There have been times, too, when 

 investigators usually "successful" with the yeast technique have reported 

 unsuccessful experiments. However, such incidents have occurred at 

 times when several or all workers in the particular laboratory were unable 

 to get positive results, and the conclusion was reached that "something 

 had gone wrong with the yeast." It is unfortunate that those working 

 with the yeast cultures in this field have not emphasized the point referred 

 to; the descriptions as published read as if it were possible to repeat 

 the work precisely as in the case of any other standard experiment. A 

 more cautious approach to the problem should at least have been 

 suggested. 



