In addition to this, of course, there must be considered the possibility of his falling considerable distances. ZOÖLOGIC CLASSIFICATION OF RATS.--The matter of accurately, systematically and scientifically cataloguing and classifying rats is one of great difficulty and is not to be undertaken by anyone but a trained naturalist. However, some of the notes we have at our disposal, gathered from many sources, may be set before the reader. It is extremely difficult to find exact correspondence of statement in the various classifications offered by writers upon plague and rats. Dr. Lantz gives the following brief classification in his section of the publication, "The Rat and Its Relation to Public Health." Order: _Rodentia._ Family: _Muridæ._ Genus: _Mus._ Species are many, but only three or four are cosmopolitan. Cosmopolitan species: _Mus rattus_--black, brown, and roof (_Alexandrine_) rat; _Mus decumanus_--gray, barn, wharf, sewer, and Norway rat. _Mus rattus_ has many varieties known throughout the world and these are named according to color and habitat. In addition to the names given in Lantz's classification, we constantly see reference to the black house rat, the brownish-gray rat (_Mus Alexandrinus_), the ordinary ship rat, the field rat, etc.; terms descriptive of habitat and appearance being very loosely applied. Little account is taken, by many, of the well-known variations in the coloration of rats due to climate and season and of the well recognized aptitude of the rat for living in-door or out-door according to circumstances of food supply, weather, etc. The "sawah" rat of Dutch India, implicated in the prevalence of plague there, was formerly considered a variety of _Mus decumanus_, but is now described as a field variety of _Mus rattus_. So too, varieties of _Mus decumanus_ are frequently named according to alleged geographic origin, habitat, color and habits, viz.: sewer rat, brown rat, Norway rat and migratory rat. The inevitable confusion bound to arise from such loose classification is obvious. Another genus, _Gunomys_ (_Nesokia_), implicated in plague, is represented in India by two species and by at least one (an undetermined one) in Java, some confusion existing in the matter as yet. Members of this genus are described as large, rough-coated rats which live both as house rats and field rats. In India the Plague Commission reported specimens of this genus as particularly susceptible to plague. In the Philippine Islands no specimens of _Gunomys_ have been observed, but _M. rattus_ and _M. decumanus_ are both present and numerous and both are subject to plague, as shown by the presence of the disease in specimens examined.