TRANSMISSION OF THE INFECTION. 155 



labored that the hair of the ifuinea pigs waved baclv and forth 

 in the breeze made by the expired air, but no cough occurred 

 durinji: the time of the exposure. The animals remained alive, 

 and did not develop plague infection. 



The results of our experiments are in accord with the well- 

 known bacteriological facts that bacteria are not detached from 

 moist surfaces by ordinary currents of air, but that when sudden 

 and forcible currents of air are forced from a distance through 

 narrow apertures as, for example, from the trachea through 

 the vocal cords, the tongue being against the gums and teeth, or 

 through the lips, as occurs in talking or coughing, that small 

 droplets of mucus, frequently invisible, may be emitted. The 

 question of whether the expired air of patients afflicted with pul- 

 monary tuberculosis was infectious was investigated particularly 

 by Niigeli and Buchner - who demonstrated that such air was 

 sterile. Fliigge and his pupils, however, demonstrated that by 

 coughing, tubercle bacilli were emitted in droplets from about 

 40 per cent of the tuberculous cases examined. Cornet and 

 Meyer ■'' after considering all of the experimental evidence con- 

 cluded that droplet infection did not play an important role in 

 the dissemination of tuberculosis. 



In pneumonic plague the conditions are very different, owing 

 to the enormous numbers of plague bacilli which are present 

 in the lungs and bronchi. In our experiments, performed with 

 cases of marked pulmonary oedema, the conditions were also 

 different. The opportunities for infection by means of the 

 droplet method must be very great in a pneumonic-plague ward. 

 The distance from the patient that the air may be infected by 

 droplets containing plague bacilli would apparently vary up 

 to certain limits, particularly with the strength of the cough, 

 the amount of mucus in the throat and larynx at the time, the 

 size of the droplets emitted, the currents of the air in circulation, 

 and the temperature * in the ward at the time. 



CONCLUSIONS. 



1. During normal and dyspnceic respiration of primary pneu- 

 monic-plague cases, plague bacilli are not usually expelled by 

 means of the expired air. 



2. During coughing of such cases, even when sputum visible 



= Die niedern Pilze, Munchen (1877), 53, 108. Centralbl. f. d. mcd. 

 Wiss. (1882), 20, 513. 



' Kolle und Wassermann, Handbuch der pathogenen Mikroorganismen 

 (1903), 1, 146. 



' See III, p. 157 of this report. 



