September 3, 1920] 



SCIENCE 



229 



IRIDIUM 



The atoms of iridium, like platinum, are in 

 face-centered cubic arrangement. 



The side of the elementary cuhe is 3.80 A., 

 and the distance from one atora to each of its 

 twelve nearest neighbors 2.69 A. 



Albert W. Hull 



Schenectady 



effects produced by x-ray energy act- 

 ing upon frogs' ova in early de- 

 velopmental stages 



Several interesting and possibly significant 

 facts were ascertained, in connection with the 

 general Study of the action of X-ray energy 

 upon the fertilized frogs' ovum, through ray- 

 ing the entire egg at different developmental 

 stages up to the time of closure of the neural 

 tube. Because of the chemical and physical 

 ontogenetic processes involving both proan- 

 lagen constituents, enzyme and nutritive, and 

 immediately anticipating tfhe morphologic fea- 

 tures of differentiation, it was supposed that 

 these substances must show a variable degree 

 of absorption of energy dependent upon the 

 stage of development. When the quantity of 

 energy utilized remained constant, the defects 

 produced should vary with the stage rayed. 

 One might anticipate 'both gross and micro- 

 scopic morphologic variations in the developed 

 embryos. The results of this experiment, how- 

 ever, are precisely of the reverse nature. 



The eggs were permitted to develop in the 

 ponds where they were laid until the proper 

 stage of development had been reached, where- 

 upon they were brought inunediately into the 

 laboratory and rayed. Development was per- 

 mitted to progress in glass jars of a capacity 

 of 1,000 c.c, the water being changed fre- 

 quently. Of the 300 eggs used for the experi- 

 ment, upwards of iifty were sectioned serially. 

 The embryos were fixed in formalin after 

 Schultze's method at varying intervals after 

 raying. None, however, was permitted to de- 

 velop to the time of metamorphosis. In aU of 

 the experiments the distance from the target 

 to the eggs and the per-second energy output 

 of the tube were constant as was also the time 

 of exposure. The tube carried a current 



strength of 50 milliamperes at 50 K.V. A 

 dosage of 100 mam. was given to each group of 

 from twenty to twenty-five eggs. These were 

 placed 17.5 cm. from the target. The different 

 groups represented approximately every de- 

 velopmental stage from the two-cell to the 

 period of the closure of the neural tube. No 

 attempt was made to orient the eggs with ref- 

 erence to the tube so that the animal pole or 

 the vegetable pole or right side or left side of 

 the embryos should be uppermost. 



Contrary to what one mig'ht at first antici- 

 pate, the developed embryos were identical in 

 every gross and microscopic detail to those 

 produced by raying the whole ovum at the two- 

 ,cell stage as described by the author in the 

 Anatomical Record of November, 1919. This 

 uniformity of results, irrespective of the stage 

 rayed, is the most striking feature of the ex- 

 periment. Sections of these embryos resemble 

 in every histological detail those produced by 

 the former method, and could serve very well 

 to illustrate the results of that investigation. 

 Since the author has already given these de- 

 tails, it would be superfluous to duplicate that 

 description in this paijer. The experiment 

 represents, therefore, still another method by 

 means of which a standardized, defective, 

 morphologic condition may be produced. 



Owing chiefly to our present lack of knowl- 

 edge of the association of chemical formula 

 with morphologic structure in the ovum, a 

 completely satisfactory explanation of this 

 phenomenon can not be given. Before such 

 may be attempted, prolonged experimentaltion 

 along this line must necessarily be carried out. 

 This represents merely one step in the experi- 

 mental analysis of the ovum and whatever 

 conclusions are drawn from the phenomenon 

 produced must be based very largely upon 

 hypothesis. 



The factors concerned fall into two natural 

 categories, one embryological and the other 

 chemical or physical, i. e., one dealing with the 

 embryological mechanism affected, and the 

 other with the nature of the change prod'uced 

 in the physical and chemical constitution of the 

 pvum. Granting the presence of a series of 

 dhemical ontogenetic modifications preceding 



