192 BACTERIOLOGY FOR NURSES 



particles in the air would be mechanically carried seems to indicate 

 that tubercle bacilli may find their way to the lung tissue by other 

 means than direct inhalation. Further, it has been demonstrated 

 that sputum exposed to direct sunlight will, especially in summer, 

 be disinfected by the time it is in a condition to be carried into the 

 air as dust. Tuberculous sputum when expectorated in shady parts 

 of the street, or in houses, or in dark places, however, constitutes 

 a real menace. It has been estimated that as many as five billion 

 tubercle bacilli may be expectorated by a single individual in 

 twenty-four hours. Consequently the neighborhood of tuberculous 

 individuals who expectorate without taking any precautions to 

 prevent the spread of infection is exceedingly dangerous. In 

 rooms occupied by such persons dried sputum containing virulent 

 bacilli may be constantly in the air blown about by sweeping, 

 walking, the closing of doors, etc. As long as sputum remains 

 moist there is no danger of infection by inhalation; the only 

 danger then lies in direct contact. 



During ordinary breathing the expirations of a patient suffer- 

 ing from pulmonary tuberculosis are normally free from bacteria. 

 In forced efforts, however, such as coughing, sneezing, and loud 

 speaking, fine particles of throat secretion are thrown out as a light 

 spray, which may be laden with organisms that may have been 

 present in the mouth. Tubercle bacilli thus sprayed may fall 

 directly on the mucous membrane of a healthy individual or may 

 be conveyed indirectly by food or other objects. 



As early as 1868, and many years before the discovery of the 

 tubercle bacillus, Chauveau suggested that the causal agent might 

 gain entrance by way of the intestinal canal. Later investigators 

 have proved beyond question that such often is the case. Tuber- 

 cle bacilli ingested in food and drink may pass through the mucous 

 membrane of the digestive tube without leaving any trace of 

 their passage, gain access to the blood, and so be carried to dis- 

 tant parts of the body. The fact that the disease usually localizes 

 itself in the lungs may be because this organ presents the least 

 resistance. It is even claimed by some authorities that no matter 

 how the tubercle bacillus reaches an individual, whether by dust 



