272 



BACILLI PATHOGENIC IN MAN. 



Futile at- 

 tempts to 

 demonstrate 

 tubercle 

 bacilli in the 



Reasons for 

 the negative 

 results. 



Modes in 

 which the 

 tubercle 

 bacillus 

 enters the 

 bodv. 



one observer (Williams) was able to demonstrate, by means 

 of the microscope, tubercle bacilli in the air obtained 

 from the ventilation shaft of a consumption hospital. 

 These failures are, however, by no means sufficient to 

 cause us to modify our convictions as to the wide distri- 

 bution of virulent tubercle bacilli or spores ; our methods 

 are, on the contrary, much too imperfect to enable us 

 to demonstrate with certainty bacilli in air, which, 

 nevertheless, when inhaled, might introduce a number 

 of these organisms into the body sufficient to produce 

 infection. The examination of air with this view can be 

 carried out by means of microscopical investigation, by 

 cultivation, or by infection experiments. As regards the 

 first method, we have already learned in the case of 

 other fungi that by means of it we can only recognise a 

 very small percentage of the bacteria which are really 

 present, and that a negative result is obtained even in 

 those cases where we are able to demonstrate the presence 

 of numerous individuals bj* means of cultivation. With 

 regard to the tubercle bacilli also, the investigation by 

 means of cultivation, which is otherwise very useful and 

 much more sensitive, cannot be employed for these 

 experiments, because, as the result of the slow and 

 difficult growth of the tubercle bacilli, the soil is always 

 completely occupied at an earlier period by other unavoid- 

 able bacteria, and also because for infective experiments 

 we require larger numbers of bacilli, and more especially 

 a more concentrated material than is obtained by these 

 investigations of the air, and hence it is not correct to 

 conclude that because infection has not occurred the air 

 investigated has been free from tubercle bacilli. Where 

 a longer time is spent in rooms contaminated by 

 phthisical sputum, &c., and where the air of these 

 rooms is breathed for some time, the entrance of the 

 respiratory tract comes into contact with many more 

 bacilli than can as yet be demonstrated by means of any 

 mode of aeroscopic investigation. 



The tubercular virus without doubt enters the body 

 most frequently with the inspired air, and this is the 

 mode in which healthy persons are most commonly 



