132 



as an index of their worth as contact sprays, since these have been 

 shown to kill by the action of their vapour rather than by the plugging 

 of the spiracles. The experiments are described and their results 

 shown in graphs and tables. The house-fly {Musca domestica) was 

 selected for the experiments as being tyj)ical and easy to breed in 

 large numbers. The toxicity of the benzene derivatives was found to 

 be similar for other insects. A comparison of the green-bottle fly 

 {Lucilia sericata, Mg.) with Musca domestica shows that house-flies die 

 more quickly from compounds with a low boiling point than green- 

 bottle flies, while the reverse is the case with compounds with a high 

 boiling point. Similarly, the cockroach, Phyllodromia germanica, L,, 

 succumbs less readily tlian the potato beetle {Leptinotarsa decemlineata, 

 8ay) to low boiling compounds and more readily to high boiling 

 compounds. This may be due to morphological differences in the 

 insects. All the benzene derivatives tested proved to be more toxic to 

 insects, molecule for molecule, than carbon bisulphide. A graph shows 

 the quantity of various benzene derivatives necessary to saturate 

 ] ,000 cub. ft. of space at 70° F., and the time required by such fpiantity 

 to kill house-flies. Carbon bisulphide at the standard rate is given for 

 comparison. As a low-boiling compound will penetrate grain better 

 than a high-boiling compound, the possibilities of xylene, chlorbenzene, 

 and brombcnzene are at once apparent, though no actual tests have 

 been made. 



For the fumigation of animals, a com])ound with a high boiling 

 point is needed, so that relatively little of the material shall be in the 

 air to be taken in by the animal, and in this respect salicylic aldehyde 

 is probably the best. As the higher animals readily oxidise this 

 substance into salicylic acid, it is suggested that it might be used for 

 internal fumigation to destroy bots. Further tests are, however, 

 necessary before selecting the most practicable substances. Up to 

 250° C. the higher the boiling point the more toxic the compound to 

 insects. Beyond 2-50° C the comjxjund is usually so slightly volatile 

 that not enough of the chemical will evaporate to be oft'ective. Lipoids 

 are very soluble in compounds with low boiling points and but slightly 

 soluble in compounds with high boiling points. Even though com- 

 pounds with low boiling points are less toxic than those with high 

 boiling points, better results may be obtained with the former, as 

 more of such compounds may be evaporated before saturation is 

 reached. 



Pierce (C. C). Combating Typhus Fever on the Mexican Border.' — 



U.S. Public Health Repts., Washington, B.C., xxxii, no. 12, 

 23rd March 1917, pp. 426-429, 4 figs. 



During the past five years migration in Mexico due to the disturbed 

 political conditions there has resulted in spreading ty])hus fever from 

 the plateau regions, where it has been endemic for many years, to all 

 parts of the country. The disease is, however, mostly limited to the 

 extremely poor and vermin-infested portion of the population. During 

 December 1915, the occurrence of three cases of typhus at Laredo, 

 Texas, caused the U.S. Public Health Service to institute measures to 

 prevent the disease from spreading to the United States and abandoned 

 disinfecting plants along the frontier were put into operation, so that 



