SUMMARY or BULLETIN No. 161 



1. There are four recognized types of tubercle bacilli; human, 

 bovine, avian, and a type that infects cold-blooded animals. Only 

 the first two types have any important part in the infection of man. 



Page 284 



2. The beaded appearance of these germs led the' early inves- 

 tigators to a belief in spore-formation. This is now known not to 

 occur. The fatty content of the bacilli varies from 10 to 42 

 percent, which is five times as much as found in any other micro- 

 organism. It appears that this fatty material has little or nothing 

 to do with the duration of their viability. Page 284 



3. The tubercle bacillus does not secrete a soluble toxin, but 

 that poisons are formed is well known. It has been shown by 

 various investigators that tubercles can be produced in test animals 

 by the injection of dead cultures. Tubercles thus produced may be 

 mistaken for those produced by living germs. Page 284 



4. A clear criterion of death is necessary in reporting results 

 on the duration of life of the tubercle bacillus. ''This fact many 

 investigators have disregarded. Page 285 



5. The tubercle bacillus may be classed with the nonspore- 

 bearing organisms as to viability ; but in this class it is one of the 

 most resistant, especially as to drying and to the antagonism of 

 decay organisms in water and foul matter. Page 286 



6. The action of sunlight upon bacteria was first studied by 

 Downes and Blunt in 1877. Numerous investigators have con- 

 tinued this study to the present day. One of the most important 

 facts brought out is that bacteria when directly exposed to the 

 sun are killed in a few minutes. This is due to the effect of the 

 ultra violet light. The ultra violet rays are now cheaply produced 

 artificially by the mercury vapor lamp. This lamp is destined to 

 play an important part in sterilization and disinfection. 



Pages 287-291 



7. It is shown by the results of all the investigators given in 

 Table 2 that tubercle bacilli when exposed directly to the sun are 

 killed in a few minutes to a few hours. The time of killing is 

 less at higher altitudes; but it is ten to fifteen times longer in 

 diffuse light. Pages 292-295 



8. Tuberculous sputum reduced to dust and inhaled by test 

 animals causes tuberculosis. A much less amount is necessary to 

 produce tuberculosis by inhalation than by ingestion. This, how- 



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