W. T. Councilman, Disease and Its Causes
“ Certain habits, on the other hand, such as kissing, which probably represents the extension of a habit of sexual origin, are disadvantageous and infection is often transmitted in this way. In syphilitic infection the mouth forms one of the most common localizations of the disease and may contain the causal organisms in great numbers. This, the spirochæta pallida, is an organism of great virulence, and man is the most susceptible animal. The disease, like gonorrhoea, is essentially a sexual disease, the primary location is in the sexual organs, and it is transmitted chiefly by sexual contact. ”
