April, '13] MORGAN AND RUNNER: ROENTGEN RAYS 229 



the direction of lialf the alternating waves, simply prevents the passage 

 of the waves in one direction, allowing the passage of the entire wave 

 in the direction desired, only half the energy put into the transformer 

 being passed through the tube. As a matter of fact, in making this 

 experiment, it was found that when a current of more than 2| milli- 

 amperes was passed through the rectifier and the X-ray tube, that 

 the rectij&er did not act positively and that current was passed through 

 the tube in both directions, setting up a condition commonly called 

 "inverse" by X-ray operators. The machine was adjusted, by 

 the introduction of a spark gap in the circuit, to a point where this 

 "inverse" just disappeared. It may be assumed, therefore, that 

 the .entire wave was passed through the tube. In other words, the 

 impulses sent through the tube were complete waves from a point 

 of very low pressure up to the maximum pressure produced by the 

 apparatus, and down again to the point of lowest pressure which 

 would pass through the tube. The tube used in this experiment 

 was quite "soft" or of comparatively low resistance. The X-rays 

 generated were, therefore, of comparatively low penetration, but of 

 great burning power. The material treated was exposed directly 

 to these highly reactive rays, and the effect produced might be expected 

 to be the maximum possible for the "soft" rays from an X-ray tube. 

 One 7-inch tube was used, material was uncovered and placed directly 

 under the tube. Distance from the target 10| inches, spark gap 

 3| inches, milliamperes 2| to 3, averaging slightly over 2|. Time of 

 exposure 2| minutes. Th^ time of exposure, owing to the construc- 

 tion of this type of machine, was about the maximum practicable; 

 and to secure this exposure 15-second flashes had to be given with 

 considerable intervals to allow the apparatus to cool. The material 

 used in this experiment (No. 14) wj\s as follows: adults exposed 18, 

 check 23; eggs, exposed 10, check 10; larvae, exposed 50, check 50; 

 pupae, exposed 10, check 10. The following gives briefly the results 

 of the examinations: adults October 29, three dead, two escaped 

 and thirteen left alive in box of exposed material, eggs had been depos- 

 ited and these were isolated for further examination; of the check 

 adults^ ten were alive and thirteen dead, check adults had also depos- 

 ited eggs which were isolated. November 8, ten of the exposed adults 

 were still alive while only five were alive in the check. Eggs had been 

 deposited in both boxes. At this examination, eggs taken from 

 boxes of exposed and check adults October 29, were hatching. 



Eggs — November 8, eggs were hatching in both the exposed and 

 the check lots. 



Larvae — November 8, both lots of larvae normal in appearance, 

 two pupae found in exposed lot and two in check lot. Shortly after 



