156 STRONG AND TEAGUE. 



to the naked eye is not expelled, plague bacilli in large numbers 

 may become disseminated into the air surrounding the patient. 



The idea that infection of doctors, nurses, attendants, etc., 

 in plague hospitals is caused entirely by particles of sputum 

 expectorated by the patient and visible to the naked eye is 

 erroneous. It follows from these experiments that the wearing 

 of masks and the proper covering of any surface of the skin 

 where fresh abrasions are present are important, personal, pro- 

 phylactic measures against plague infection. It also follows 

 that the eyes should be protected against this manner of con- 

 junctival infection by proper glasses. 



Articles of clothing worn in the wards should be sterilized 

 immediately after removal, since plague bacilli may be present 

 even though no particles of sputum may be visible upon them. 



From these experiments, also, it is evident how dangerous 

 an infective agent a pneumonic-plague patient is. In no other 

 disease is the individual so dangerous and in no other disease 

 does the danger from droplet infection approach that which 

 exists in pneumonic plague. The number of plague bacilli ex- 

 pelled in droplets from pneumonic-plague cases is probably far 

 greater than the number of bacilli ever expelled by patients 

 afflicted with tuberculosis, croupous pneumonia, diphtheria, or 

 influenza. 



MANNER OF SPREAD OF THE DISEASE DURING THE EPIDEMIC. 



During the epidemic the disease was evidently spread directly 

 from man to man by droplet infection and by the more or less 

 intimate contact of healthy individuals with an infected person. 

 Whatever may have been the primary source of the epidemic, 

 its dissemination occurred entirely independently of tarbagans, 

 rats, donkeys, or any other animals.^ 



The disease was introduced into uninfected villages and towns 

 by the importation of individuals infected with pneumonic plague 

 or by those in the incubation period of this disease. No definite 

 bacteriological evidence, that healthy carriers of the disease 

 with plague bacilli in their sputa existed during the epidemic, 

 has been produced. We had opportunity to examine two healthy 

 individuals who were supposed to have given rise to the disease 

 in other persons but who themselves remained healthy. We 

 were unable to demonstrate any plague bacilli in their sputum, 

 and it was not infective for guinea pigs. 



' For evidence regarding dissemination by donkeys, see VIII, p. 225 of 

 this report. 



