62 W. M. BALDWIN. 



tion tolerated by the organism followed by a dilution as above 

 was ascertained. In the instance of trypanblau, trypan red, 

 isamine blau, and neutral red, this was found to be eight volumes 

 of the water solution of the stain to two of the culture. The 

 stock solution contained o.ooi gm. of the dry stain to 200 c.c. 

 water. Staining of the paramcecia cultures from one and one 

 half to two hours at the room temperature brought about the 

 appearance within one half hour of a deep globular coloration of 

 the cytoplasm of the organism. The subsequent dilution of this 

 stained culture, through the addition of ten volumes of water 

 to one of the culture, prevented subsequent injury, so that the 

 vitality of the organisms remained unimpaired for a period of 

 eight days. The nucleus did not become stained nor was the 

 motility lessened. Ordinarily, the specimens were not studied 

 for a period longer than eight days. With a few, however, 

 observation at the expiration of fourteen days demonstrated 

 still actively motile paramcecia with unstained nuclei. Beyond 

 these limits no effort was made to ascertain either the varying 

 degrees of rapidity of absorption for the different stains or the 

 exact limit of absorptive capacity of the organisms for any 

 particular stain. The dilutions above-mentioned were arbi- 

 trarily selected, since with these as a constant, the most marked 

 reactions to X-ray energy were obtained. 



The next step in the experimentation consisted of a deter- 

 mination of the amount of X-ray energy necessary to cause the 

 death of unstained organisms. The source of energy was a 

 special Coolidge tube actuated by 35 K.V. with a current strength 

 of 2.0 milliampere and cooled by an airblast. Since the total 

 diameter of the tube was only 7.0 cm. the paramcecia cultures 

 could be placed in ordinary watch glasses at a distance of 8.5 cm. 

 from the center of the target. They were protected from the heat 

 rays arising from the tube by means of three spaced-layers of 

 carbon paper. Numerous experiments showed that there was 

 hardly any loss through evaporation during the raying. 



A quotation from the notes will illustrate the general experi- 

 mental results observed. On the morning of May 5, 1916, a 

 series (A) of six cultures, each consisting of numerous unstained 

 paramcecia, was rayed under the conditions mentioned above 



