Pyorrhea dentalis and alveolaris is one of the most prevalent diseases of man. In our studies we have found it present to some extent in more than 95 per cent. of all adults examined. Something of its importance may be suggested by the fact that more than half of all the permanent teeth lost are lost from this disease. Each tooth lost represents a suppurative process in the mouth of at least a few or usually many years. It can hardly be possible that the harmful effect of such a disease is local only. Loss of the teeth alone is an important thing in the life of any individual. We feel quite certain that the great prevalence and importance of pyorrhea alveolaris is not now generally appreciated, even among the medical profession. The specific cause of pyorrhea dentalis and alveolaris is endamebas.1These protozoa have been known for more