EFFICACY OF VARIOUS MASKS. 267 



General discussion. — The protocols which have been cited could 

 be supplemented by liumerous others'" giving similar results. 



While these experiments furnish evidence that fine droplets 

 of sputum of patients suffering from pneumonic plague may 

 pass through the mask that was so widely used in Manchuria, 

 yet they do not at all indicate that this mask was entirely 

 without value. Obviously, the mask would hold Vjack gross visible 

 particles of sputum which are sometimes thrown out in coughing. 

 Moreover in our experiments, when prodigiosus bacilli were 

 recovered from the nostrils, it is probable that in the same test 

 without the mask far greater numbers would have entered; in 

 other words, it seems probable that great numbers of bacteria, 

 that otherwise would have entered the nose and mouth, remain 

 on the surface of the mask and in its substance. 



Hence we believe that masks should be worn by those attending 

 pneumonic-plague patients, but that they should not be regarded 

 as affording absolute protection against infection; bearing this 

 in mind, even when masked, one should remain in the near 

 vicinity of the patient only so long as is necessary for the work 

 in question. 



CONCLUSIONS. 



(1) The "Mukden mask" in general use during the epidemic 

 of pneumonic plague in Manchuria, during the winter of 1910 

 to 1911, does not prevent the passage into the mouth and nostrils 

 of B. prodigiosus when contained in small droplets sprayed 



' The Mukden mask was used in 42 tests and was found to hold back 

 the prodigiosus bacilli in only 6 of these and to allow them to pass in 36 

 instances. Of the 6 tests in which the bacilli failed to penetrate the mask, 

 three were preliminary experiments to determine whether a satisfactory 

 spray was produced in talking or coughing after rinsing the mouth with 

 a suspension of pi'odigiosus bacilli; plates exposed during the experiment 

 showed less than 20 colonies each and the method was therefore abandoned. 

 In two others of these 6 tests the exposed plates showed only 15 and 200 

 colonies respectively. Finally, in the last of these 6 tests, the subject 

 drew the cotton from before his mouth and nose into his mouth where it 

 became saturated with saliva and plates were not made from the cotton 

 within the nostrils. 



In some of the tests in which the prodigiosus bacilli passed through 

 the Mukden mask, the exposed plates contained only a few colonies, in- 

 dicating that the test was much less severe than those in the protocols 

 recorded above. 



Our Canton flannel Broquet mask was employed in 17 different exper- 

 iments. It held back all the prodigiosus bacilli in 10 of these and allowed 

 some of them to pass in 7. 



