BACILLUS TUBERCULOSIS. 271 



From the knowledge which we have obtained, as the Deductions as 

 result of experiments, with regard to the biological g^fa"^ 6 

 relations of the tubercle bacilli, important conclusions may tuberculosis, 

 be drawn as to the mode of spread of these bacilli, and of 

 the disease caused by them. In our ordinary surround- 

 ings the conditions necessary for the multiplication of 

 the tubercle bacilli are, without doubt, never present ; 

 in other words, they do not possess a saprophytic stage 

 of existence, but they always behave as true parasites 

 under the conditions which are present in nature. 

 Hence the spread of tuberculosis could only occur by 

 infection from individual to individual, were it not that 

 the bacilli can retain their vitality and all their virulent 

 characters for a considerable time outside the body. This 

 preservation of the organisms is aided to a great degree 

 by the presence of spores, which have proved, as the 

 result of direct experiments, to be very resisting. 

 Sputum, containing spore-bearing tubercle bacilli, was Length of life 

 still virulent after six weeks, although it was kept moist, f tjje tubercle 

 and although putrefaction occurred in it ; such sputum 

 when dried retained its virulence up to 186 days, as was 

 proved by the inoculation of guinea-pigs. Hence we 

 may assume that our ordinary surroundings must be 

 frequently much contaminated with virulent bacillus 

 spores, and that infection can occur not only directly 

 from the patient, but also by means of the most various 

 objects from his surroundings, often in a very indirect 

 manner and after a relatively long time. The most Distribution 

 important source of the contamination of our surround- by means of 

 ings with tubercle bacilli is undoubtedly phthisical 

 sputum; as almost one-seventh of mankind die of 

 phthisis of the lungs, and as a large portion of tho 

 sputum is constantly dried in the clothes and on other 

 objects, and thus is able to pass into the dust, the 

 distribution of the virulent material must be compara- 

 tively great. 



Nevertheless numerous experimenters have failed to 

 discover any tubercle bacilli in the air, even of places 

 such as wards in which phthisical patients were con- 

 stantly present (Celli and Guarneri, Bellinger), and only 



