ever, must not be taken to indicate that inhalation plays a more 

 important part than ingestion as a cause of tuberculosis. The 

 more important method depends upon the opportunity of infection 

 from each. Investigators do not agree on this question. At pres- 

 ent both inhalation and ingestion should be considered dangerous 

 sources of tuberculous infection. Pages 295-306 



9. The Mills-Reincke phenomenon, which has been given a 

 mathematical equivalent by Hazen's theorem, viz., " Where one 

 death from typhoid f ever t has been avoided by the use of better 

 water, a certain number of deaths, probably two or three, from 

 other causes have been avoided," has been found by Sedgwick and 

 MacNutt to be sound and conservative. Their studies show that 

 tuberculosis has decreased in certain cities of Massachusetts, which 

 decrease is evidently due, in part, to the improvement of their 

 water supply. Pages 307-308 



10. It is reported in the literature that tubercle bacilli live for 

 a very long time, several months to more than a year, in water and 

 other material. Pages 309-310 



11. In experiments to determine the time that tubercle bacilli 

 live in various conditions the chief difficulty is the "index of 

 death" for these germs. This is true since cultivation of the 

 tubercle bacilli from contaminated material is not feasible, and 

 since the dead germs produce, in test animals, tubercles indistin- 

 guishable by microscopic appearance from those produced by live 

 tubercle bacilli. Pages 311-313 



12. Pure cultures of nonspore-bearing organisms and the vege- 

 tative cells of spore-bearing germs when exposed to direct sun- 

 light in thin smears are killed in */? to 6 minutes ; the human, 

 bovine, and avian types of tubercle bacilli exposed in the same way 

 were killed in i to 4 minutes. Pages 314-317 



13. When exposed to desiccation in a dark, well-ventilated 

 place, the nonspore-bearing organisms and the vegetative cells of 

 spore-bearing organisms died in i to 4 days; spores of B. siibtilis 

 and B. vulgatus' used as controls were not killed in 35 days; the 

 human and bovine type of tubercle bacilli exposed at the same time 

 and under the same conditions were dead within 4 and 8 days re- 

 spectively. Pages 317-318 



14. Pure cultures of bovine tubercle bacilli mixed in cow 

 manure and exposed in a two-inch layer in a pasture field in the 

 sunshine remained alive and virulent for two months. 



Pages 323-3-24 



280 



