The accompanying photomicrographs of sections of the human tongue show it to be covered with glands, fissures, and spinous processes, the latter slanting at a great angle. It is evident that this surface may hold pabulum and protection for the development and growth of myriads of bacteria. It is possible that cavities in the teeth, and gums diseased from deposits about the teeth, are more prolific, but probably not.
Out of the "seven nutrient media for bacteria in the oral cavity" given by Miller, five are always present on a coated tongue, namely, normal saliva, buccal mucus, dead epithelium, particles of food, and exudations from diseased gums.
Formerly physicians were very careful about the examination of the tongue, but at present the diagnostic value of its coating is largely disputed. On the other hand, some of the best physicians make the tongue the principal basis of their diagnosis, especially in
FLETCHER HM. THE TONGUE AS A BREEDING PLACE FOR BACTERIA.. JAMA. 1901;XXXVII(3):170-172. doi:10.1001/jama.1901.62470290016002c