There would be but little extension of the hookworm disease in a community where shoes were worn and the habits were cleanly.
It is by no means improbable that the formation of the habits of civilization was influenced by infection.

Most of these habits, such as personal cleanliness, the avoidance of close contact, the demand for individual utensils for eating and drinking, are all of distinct advantage in opposing infection.

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 _spirochaeta 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.