PARASITES AND DISEASE (VEGETABLE PARASITES) 161 



Etiology. The exciting cause is the diphtheria bacillus. 

 The frequent presence of the germ in healthy throats in- 

 dicates the necessity of predisposing causes, among which 

 are lowered resistance and personal susceptibility, en- 

 larged tonsils, pharyngitis, laryngitis, etc. Infection may 

 occur from food, especially milk, from books, toys, from 

 persons in contact with the disease, and from healthy 

 carriers of the bacillus: Age is important. Sucklings 

 are very slightly susceptible. From the second to the 

 fifth year the susceptibility increases, then gradually 

 decreases. 



Morbid Anatomy. This is essentially a local disease 

 of the larynx, pharynx, or nose, with systemic and vis- 

 ceral lesions due to the absorption of the toxins. Locally 

 there is produced upon the mucous membrane at the 

 site of infection a false membrane. There is necrosis 

 of the epithelium, followed by an inflammatory exudate 

 rich in fibrin, which, in conjunction with the dead epi- 

 thelial cells, form the false membrane. The germs grow 

 and develop upon the necrotic tissue and not upon the 

 living tissue. Removal of the false membrane leaves 

 a raw and bleeding surface beneath, the depth to which 

 the tissues are affected depending upon the amount of 

 necrosis. This membrane may block the nasal passages, 

 extend to the conjunctiva, and through the Eustachian 

 tubes to the middle ear. 



It may block the larynx or extend into the trachea or 



bronchi. The internal lesions are due to the toxin, as 

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