Yes, you most certainly can. Anyone who says otherwise is not properly educated on this topic. You can transmit herpes, gonorrhea, thrush (which is a yeast infection), mononucleosis, and some others through any kind of oral contact. Your partner must already have the infection in their mouth to transmit these ailments to your mouth. You can't catch oral gonorrhea by "french kissing" someone who's only got the genital version of the disease.