SCIENCE-SUPPLEMENT 



poisaning was decided upon as the one effective 

 plan. The TI. S. army stationed in the islands 

 had offered assistance in the way of poison gas 

 experiments, as it realized the seriousness of the 

 plague situation, 



C. E. Pemberton, assistant entomologist at the 

 sugar planters' experiment station, was assigned 

 to investigate this possible means of control, but 

 he reported: 



"The use of gas in any form for combatting 

 rats in tihe cane fields is wholly impracticable. 

 Rat burrows, deep, extensive and permanent, are 

 common, but extremely difficult to find until the 

 cane has been cut and the trash burned. By then 

 the rats have left the burrows. A minute search 

 in any field, before harvesting, would reveal most 

 of the rat burrows present, but the time required 

 for such work would be far too great to warrant 

 such a procedure. ' ' 



Trapping was also experimented with and found 

 unsuitable for use over so large an area. 



The board of health is leaving the experimental 

 work to the sugar planters, and is using its ener- 

 gies in cleaning up rat infested places in the 

 labor camps. The people of Hamatua are giving 

 the board every assistance in ridding tlie district 

 of the menace. Camps are being cleaned up, rub- 

 bish is being burned and intensive tra.pping is 

 conducted around houses and barns. All stray 

 dogs and cats have been killed as it has been 

 found that they also are capable of carrying the 

 plague. 



MESOTHORIUM 



U. S. Bureau of Mimes 



The chemistry of mesothorium, the radio-active 

 element found in monazite sand and other tho- 

 rium minerals, which is used as a substitute for 

 radium in the manufacture of certain luminous 

 paints and for medicinal purposes, is discussed 

 in Technical Paper 265,byHerman Sehlundt, just 

 issued by the United Staites Bureau of Mines. 



Among the thirty-odd radio-active elements, 

 mesothorium, the first product of thorium, ranks 

 next to radium in importance, stajtes the author. 

 Like radium, its disintegration products emit the 

 three types of radiation that are characteristic of 

 radio-acitave substances and that are Imown as 

 alpha, beta and gamma rays. Mesothorium decays 

 at least 250 times fasiter than radium, and hence 

 in the pure state its activity, weight for weight, 

 would greatly exceed that of radium. Although 

 itself rayless, its first product, which is rapidly 

 formed after mesothorium has been separated, 

 gives a powerful beta and gamma radiation; the 



alpha radiation of freshly prepared radium at- 

 taias a maximum within a month, whereas that 

 of mesothorium increases comparatively slowly, 

 and reaches its highest point during the fifth year 

 after separation. Mesothorium preparations 

 therefore must be "aged" before their full 

 alpha-ray effect is realized in luminous -products. 



During the first years of separation, notwith- 

 standing the comparatively rapid decay of meso- 

 thorium, its preparations maintain a higher 

 gamma-ray activity than an equivalent quantity 

 of radium. Mesothorium may thus serve as a 

 substitute for radium, both in luminous com- , 

 pounds of radium and for therapeutic purposes. 



Uranium ores, especially caruotite, are worked 

 primarily for the extraction of radium — uranium, 

 vanadium, etc., being secondary products. Meso- 

 thorium, on the other hand, is obtained as a sec- 

 ondary product or a by-product in the manufac- 

 ture of thorium for the gas-mantle industry, its 

 output being governed by the demand for thorium 

 nitr.ate. 



For a good many years the production of meso- 

 thorium in Germany, and to some extent in other 

 countries in Europe, has kept pace vsTith the pro- 

 duction of radium. The Germians early recog- 

 nized the value of mesothorium as a substitute for 

 radium, not only for luminous paint but also for 

 medical purposes. Only during the last two or 

 three years, however, has production taken place 

 in this country. Two companies have been recov- 

 ering mesothorium as a by-product in the extrac- 

 tion of thorium. The Bureau of Mines has had 

 a cooperative agreement \vith one of these com- 

 panies. Very little has been published concerning 

 the recovery of mesothorium. Methods of meas- 

 urement have been uncertain and somewhat diffi- 

 cult, and Dr. Schlund 's paper is intended as a con- 

 tribution to the chemistry of this iiseful and inter- 

 esting element. 



Experiments of the Bureau of Mines in deter- 

 mining the ratio of mesothorium to thorium by 

 direct comparison' of gamma activity with radium 

 are described in this paper. 



WOULD REQUIRE PEDESTRIANS TO SIGNAL 

 AUTO TRAFFIC 



Science Service 

 Signals by pedestrians to show automobile 

 drivers .their street crossing intentions were pro- 

 posed here to-day by Dr. Raymond Dodge, chair- 

 man of the psychology section of the National 

 Research Council, as a means of making city 

 traffic more safe. 



