abstracts: bacteriology, technology 495 



was carried out to determine the extent of immunity three years after 

 the subsidence of the epizootic in the city. An attempt was also made 

 to determine the relative susceptibility of rats of different sizes, and the 

 susceptibility to varying doses of culture. It was found that three 

 years after the epizootic many of the rats found in San Francisco were 

 immune to plague. The size of the rats was found to be of compara- 

 tively little importance in determining the success of the inoculation 

 but the dose of the culture had a very marked influence. G. W. M. 



BACTERIOLOGY. — Susceptibility of a ground squirrel (Ammosper- 

 mophilus leucurus, Merriam) to plague. George W. McCoy and 

 Charles W. Chapin. Public Health Bulletin No. 53 U. S. Public 

 Health Service, 1912. 

 Ammospermophilus leucurus is a small ground-squirrel found in Cali- 

 fornia. Nine of the rodents were used for the purpose of determining 

 their susceptibility to plague. The experiments proved fatal in every 

 case and in the majority a high degree of plague septicaemia developed. 



G. W. M. 



TECHNOLOGY. — Physical testing of mechanical rubber goods. Circu- 

 lar No. 38, Bureau of Standards. 1912. 



This circular outlines the methods used at the Bureau of Standards 

 for determining the physical properties of rubber and gives a brief 

 description of the processes of manufacture, beginning with the col- 

 lection of crude rubber, and including processes for reclaiming rubber. 

 The tension test is the most widely applicable, being used to determine 

 the more important physical properties such as elasticity, strength, 

 and ultimate elongation. Machines and apparatus for conducting these 

 tests have been designed and constructed at the Bureau of Standards. 



In preparing samples for test a die is used which insures uniformity 

 of size. Gage marks are placed on the. test piece from which the per- 

 manent set and ultimate elongation are measured. Results of tests 

 are shown graphically, illustrating the characteristics of various rubber 

 compounds. The effect of continued heat at 160°F. on different rub- 

 bers is shown and these tests are being extended with a view to estab- 

 lishing an accelerated aging test. An analysis of the distribution of 

 stress in a ring test piece is given showing that as a result of the uneven 

 distribution of stress the ring method does not develop the full tensile 

 strength of rubber. This result has been verified by tests. 



P. L. Wormeley. 



