28 ESSAYS ON BACTERIOLOGY. 



that the supposed hereditary acquisition of tubercu- 

 losis resolves itself into the results of association of 

 cases, in other words, post-natal infection. Others 

 hold to the view which commonly prevails; while 

 some endeavor to explain the facts upon the theory, of 

 which Baumgarten is the chief exponent, .that the 

 bacilli received by heredity often remain latent for 

 months or years, springing into activity with the rise 

 of conditions favorable to their growth. Evidently, 

 more light must be obtained before the problem can 

 be solved, and bacteriology has stepped in with an 

 offer of aid; first, by showing what is the actual cause 

 of the disease, and leading in the search for this defi- 

 nite material thing in the body of the fetus. The 

 greatest interest has centered around tuberculosis, for 

 obvious reasons. 



I do not propose to enter here into elaborate details,, 

 but simply to indicate the lines along which the inves- 

 tigations have run. The search has been made by 

 microscopic examinations, by cultivations, and by in- 

 oculation experiments. Thus, a number of female 

 animals are inoculated with tuberculosis. They are- 

 bred, if not already pregnant. Only the fetuses of 

 such mothers as can be proven to have the disease are 

 used. Their bodies being carefully pi'otected frora 

 contamination, the following experiments are made 

 upon them: They are examined microscopically, cul- 

 tures are made from them and portions of their bodies 

 are inoculated into healthy animals. The cultures 



