EFFECT OF ULTRA-VIOLET RAYS. 385 



ultra-violet radiation, that protozoa and the ova ■ or larvse of intestinal 

 ■worms may all be killed by this powerful agent. It has been shown (3) 

 that radium emanations on short exposures inhibit, and on longer expo- 

 sures kill various forms of bacteria, protozoa, ova, embryos, and larvge. 

 The only reference we have found indicating that the effects of ultra- 

 violet rays have been tested with protozoa is an article by HerteK*) 

 showing that paramoecia are killed by these short length waves. We have 

 failed to find in Manila any reference indicating that the influence of 

 ultra-violet rays on amoebae has been investigated. 



These considerations seemed to indicate the desirability of studying 

 the effect of ultra-violet rays on amcebge and the experiments about to 

 be described were undertaken for this purpose. The source of the ultra- 

 violet radiations used by us was a quartz mercury-vapor arc lamp owned 

 by the Bureau of Science in Manila. This lamp, which was made by the 

 firm of W. C. Heraeus, Hanau, Germany, was rather small for our 

 purpose, but produced a brilliant light particularly rich in ultra-violet 

 rays. A description of the lamp may be found in the Zeitschrift fiir 

 Electro-chemie. ( 5 ) 



The strain of amoebae used was originally isolated from a normal 

 human stool, has been kept constantly under cultivation for a year, and 

 is the same that was employed previously to determine the efficacy of the 

 ipecac treatment of dysentery. (6) These amoebae belong undoubtedly 

 to a free-living species, but it is believed that any agent which is found 

 to be detrimental to the growth of such free-living organisms will prove 

 even more efficacious against the parasitic amoebae which are much more 

 susceptible to unfavorable conditions as shown by the fact that it has 

 hitherto been impossible to cultivate them on artificial media. 



The experiments were performed in a number of ways, using both 

 solid and fluid media, and with exposures for different periods of time 

 at various distances from the source of radiation. After the exposure, 

 cultures were made at once from the exposed amoebae to deteimine whether 

 they had been killed by the rays, and these observations were controlled 

 by similar cultures made from amoeba grown under identical circum- 

 stances, but which had not J)een subjected to the action of ultra-violet 

 waves. The effect of the rays on the amoebae has also been compared 

 with the effect produced on Bacillm typhosus and Bacillus dysenterice 

 (Shiga) by similar exposures. Before proceeding to an account of the 

 experiments themselves we will give a brief description of the stock 

 culture of amoebae and the plates used, and the method of exposing the 

 cultiires to the rays. 



A. Stock culture of amosbce. — The amoebae referred to previously were cultivated 

 for several weeks in a 250 cubic centimeter Erlenmeyer flask containing plain 



