882 RADIATION BIOLOGY 



graphs.) The numbers of afflicted animals are small but assume impor- 

 tance in comparison with the results of other workers. 



Warkany and Schraffenberger (1947) studied litters from 108 rat 

 females irradiated on any one of days 9 to 15 of gestation (referred to by 

 the authors as "10th to 16th" days) 6 and reported well over a dozen 

 different abnormalities. Unfortunately they do not separate the results 

 for different doses but give only the dose range (often very wide, e.g., 

 190-900 r) for each stage group. Since, at any one stage, an increase in 

 dose generally increases percentage incidence of a given abnormality 

 (Russell, 1950), it is obviously impossible to determine the most sensitive 

 stages in Warkany and Schraffenberger's experiment by comparing inci- 

 dence : for a peak may be due merely to a higher dose having been used. 

 Moreover, since, by raising the dose, a primordium or process can usually 

 be affected on days adjacent to that of maximum sensitivity (Russell, 

 1950), it is not surprising that with the large doses used (up to 1120 r) the 

 authors did not usually get very clearly defined critical periods. Even 

 so, a few emerge when incidences are calculated from their report and 

 when allowance is made for the dosage difficulties discussed above (see 

 Figs. 13-4 to 13-7). Thus, the peak for rib angulation is definitely on 

 day 14, the long bones of the front legs are sensitive almost exclusively on 

 day 12, and those of the hind legs mostly on day 12 except for the tibia 

 which has a peak sensitivity on day 10. These points and others become 

 interesting in comparison with other experiments (see pp. 891-893). 



Like Kaven, Russell (1949, 1950) used genetically uniform mice, in her 

 case an Fi hybrid between two inbred strains to add vigor to uniformity. 

 The scope of the experiment was extended with respect to ( 1 ) the number 

 of stages surveyed, (2) doses used (200 r for all stage groups, 300 and 

 400 r at certain ones), and (3) types of abnormalities observed. The 

 skeleton was chosen for detailed study mainly because its various parts 

 are formed by processes whose periods of maximum activity, taken 



6 See footnote 3. 



Figs. 13-4 to 13-7. Results of several groups of investigators represented to show 

 critical periods for the induction of various abnormalities. 



Wherever sufficient data are given in the original publication, representation here is 

 by (a) percentage incidence of abnormality (see scale in figures) and (b) magnitude of 

 dose required to produce abnormality. Thus, the wider and more heavily shaded a 

 band, the greater the sensitivity. Absence of a band at a particular stage indicates 

 that the abnormality did not occur in the irradiated group (see, e.g., 200 r results of 

 Russell), except where the serrated end of a band indicates that the dose series was 

 not continued to the stage in question (see, e.g., 300 and 400 r results of Russell, all 

 results of Wilson and Karr). For cases where exact incidence for a given stage and 

 dose cannot be calculated from the original data, representation is only roughly 

 quantitative. In general, + = 1-49%, >200 r; + + = 1-49%, 1-200 r; + + + 

 = 50-100%, >200 r; + + + +=50-100%, 1-200 r. (J = Job, Leibold, and 

 Fitzmaurice, 1935; K = Kaven, 1938a,b; R = Russell, 1950, 1949; Wi = Wilson and 

 Karr, 1951, 1950; Wa = Warkany and Schraffenberger, 1947.) 



