216 CLINICAL BACTERIOLOGY. 



distinctly a greater susceptibility than adults, but this grows 

 less after the fifth or sixth year. 



The portal of infection for the diphtheria-bacillus 

 may be constituted by any mucous membrane, as that of 

 the nose, the pharynx, and the larynx, as well as that of 

 the vagina, the conjunctiva, etc., and, further, every wound- 

 surface. The larger number of cases of diphtheria are at- 

 tributable to direct association with diphtheria-patients. 

 The diphtheria-bacilli may, under such conditions, gain en- 

 trance into the pharynx, where infection takes place most 

 commonly ; as well as with the food and by way of the air- 

 passages. The diphtheria-bacillus is probably not carried 

 great distances through the air. It has never been found 

 in the air, and it is rather sensitive to drying in a thin layer. 

 In thicker layers the bacilli may survive for four months, 

 and if the diying be incomplete, for seven months. Proba- 

 bly the bacilli are conveyed directly through the agency of 

 the portions of membrane coughed up by the patients. In 

 some cases eating-utensils and drinking-utensils, handker- 

 chiefs, toys, etc., have been the means of conveying the 

 disease-germs from children suffering from diphtheria, as 

 well as convalescents. Children may also be infected by 

 adults through kissing, if these have suffered from a harm- 

 less angina clinically free from diphtheric characteristics. In 

 other cases direct infection can absolutely not be demon- 

 strated, and at times such an occurrence can be actually 

 excluded as, for instance, when the first case of diph- 

 theria occurs in a village cut off from all communication 

 with the external world. Under such circumstances it must 

 be concluded that the diphtheria-bacilli have been derived 

 from a case of diphtheria that pursued the clinical course 

 of a benign angina and gave rise to no suspicion of diph- 

 theria ; or from a case already cured, in which the bacilli 

 may be present for a long time after the disappearance of 

 all symptoms (p. 230) ; or the conjunction of special cir- 

 cumstances has, in accordance with the theory of Roux and 

 Yersin, endowed with virulence pseudo-diphtheria-bacilli 

 that have been present in the mouth of- the infected indi- 

 vidual. What conditions may bring about this circum- 

 stance, or whether it is at all possible, is not yet known. 

 On the other hand, it is known, from an observation in 

 which virulent bacilli were found in the mouth of a healthy 

 child, that a certain predisposition, a lesion of the mucous 



