The saliva of dogs is not sterile (that is, devoid of bacteria), although with some primitive peoples it was customary to have dogs lick their wounds to disinfect them. In fact, in the saliva of dogs, and of other animals, there are substances, such as the lysozyme protein, which have bacteriostatic functions, that is to control, even if not completely eliminated, the populations of bacteria. Their function is to maintain a balanced situation in the mouth, in which non-sterile substances continuously enter, think of foods, without having infections. It is clear, however, that the saliva of a sick dog, like that of a sick person, can still cause disease, the most famous of which is rabies.