228 TEXT-BOOK OF BACTERIOLOGY. 



or oval, but, on the contrary, contain contracted walls, and do not. 

 present bi-convex, but bi-concave surfaces. Since the bacteria found 

 in pure cultures do not possess greater power of resistance than 

 non-sporulating bacteria, but on the contrary are destroyed by a 

 low degree of heat 70 to 80 C. it will not be erroneous to recog- 

 nize these appearances as eventually due to vacuolation or some- 

 thing quite similar. 



Noteworthy and highly significant in a practical way is the fact 

 that the bacilli themselves without sporulation are capable of re- 

 sisting destructive influences to an unusual degree. Tubercular 

 sputum as an example composed of thick albuminous matter which 

 especially protects the bacteria against destruction will withstand 

 drying for months, temperatures near the boiling point, the action 

 of the gastric juices, and also the influences of the strongest de- 

 composition, without the least curtailment of its infectious activity. 



The tubercle bacillus shows in its staining a marked peculiarity 

 referable to its exceptionally compact and impenetrable skin or 

 envelope, which offers an obstinate resistance to the penetration of 

 the staining- fluids. This explanation will be permitted because of 

 the obstinacy which the bacillus also shows under other conditions. 

 The actual presence of spores is not necessary to this bacillus in 

 order to perpetuate itself. This need not in any way conflict with 

 the circumstance that we may through further investigations dis- 

 cover actual spore-formation. 



The tubercle bacillus is an anaerobic bacterium. It is a strictly- 

 parasitic micro-organism that can only with difficulty be cultivated 

 outside of the body, and is very selective in regard to its culture 

 medium, thriving slowly under all conditions and especially re- 

 stricted in its development to narrow ranges of temperature. 

 Small deviations of temperature from the required blood heat (37 

 C.) suffices to wholly retard its increase. 



The demonstration of tubercle bacilli in unstained preparations, 

 is associated with great difficulty, still it is possible, and undoubt- 

 edly at about the same time that Koch published his investigations- 

 concerning the causes of tuberculosis, Baumg-arten had also seen 

 the same bacillus in unstained preparations and recognized its sig- 

 nificancethough of course without being 1 able even remotety to 

 bring* conclusive proofs of his discovery, which rendered Koch's 

 communications so highly valuable. 



Koch first concluded from the striking relations of this bacillus, 

 to staining that it should be regarded as a peculiar kind. With 

 our usual watery or diluted alcoholic anilin stains the bacilli are 

 not stainea at all, and it was due to this fact that the germ evaded 



