as regards etiology, symptoms, diagnosis, and treatment, has been completely revolutionised and placed on a sound, and, it may be, hopeful, basis. We now know that the sleeping sickness is a terminal phase of a trypanosome infection—a type of disease hitherto unrecognised in human pathology—that the immediate cause of the sleeping symptom is an infiltration of the lymphatic spaces of the brain with certain small mononuclear cells, that the disease is conveyed by the tsetse fly, and that it is amenable to some extent to arsenic, mercury, and certain dyes—all absolutely recent discovery.
Turning to the next chapter in Davidson, we are obliged to remark that the battle is still in progress as to whether yaws is syphilis or an entirely independent disease. Castellani's recent discovery of a spirochete in yaws, though interesting, has by no means solved the question.
In connection with the subjects of the next four chapters of Davidson, much work has been done and is going on; but it is to be regretted that these strenuous efforts have not proved more fruitful. The tropical fluxes—diarrhoeas and dysenteries—in the aggregate constitute, I believe, the most important department of tropical medicine. Unfortunately they are still, both as regards etiology and treatment, in an unsatisfactory state. It is true that the amoeba is creeping into favour, and that we have got the length of recognising a bacillary dysentery; but the amoeba and the bacillus dysenteriae do not, I feel sure, cover the entire field, and, unfortunately, the knowledge of their existence, although it may have done a little for diagnosis, has not materially strengthened our powers of treatment.
Sprue remains a mystery. It is a specific disease undoubtedly, but the specific element has not been detected. On the other hand, the specific relation of the amoeba to a certain type of dysentery and to liver abscess may now be
