22 ESSAYS ON BACTERIOLOGY. 



Without following the details of th^s subject fur- 

 ther, it may be said that our ideas of the durability of 

 infectious material have become more definite, the 

 lines of investigation have been much more sharply 

 defined, additions of much practical value have been 

 made to our knowledge, and we have reason to expect 

 more light in the near futiire. To illustrate what has 

 been done: It has been shown that the gonorrheal 

 poison rapidly loses its virulence; after even a short 

 period of drying outside the body it can neither be 

 cultivated nor inoculated. On the other hand, the 

 ordinary pus germs have been found to be very ten- 

 acious of life. Rosenbach, to whom we owe most of 

 our knowledge of them, has found them active after 

 two years in. a culture tube. 



But far and away beyond anything in this line is 

 the discovery that the essential infecting agent in tu- 

 berculous material may maintain its vitality for 

 months, even in a dried state, and not only its vitality, 

 but also its malevolent infectious character. Upon 

 this fact is based one of the most important discussions 

 which is at present agitating the medical and sanitary 

 world. 



Closely connected with this problem of the durabil- 

 ity of infectious material is the question: How and 

 by what channels is it carried? Here, again, a large 

 part of our knowledge antedates bacteriology. But 

 the older methods were difiicult, slow, and often un- 

 certain, and not infrequently, while furnishing most 



