so inevitably does the jargon of a branch of science flourish in the thought and on the lips of those who devote themselves to that branch, and bind them in a sort of freemasonry. We do not expect cricketers or golfers to talk in plain English; why should we expect chemists or naturalists to do so? After all, it is a question of moderation and of gradually increasing the dose. The beginner must not be terrified by an array of outlandish words. 30. _Rats and the Plague_ Rats! Who said rats? That is an important question, because the word means different things to different people. To some persons “rats” means simply “nonsense”! To Sir James Crichton Browne it means the devastator of stores and the dread carrier of bubonic plague. To the naturalist it means a group or natural cohort of small mammals similar to our common rat and mouse, representatives of which are found in every quarter of the globe and in almost every island of the sea. The distinct “kinds” or “species” are numbered by the hundred. They are extraordinarily alike, and can only be distinguished and classified into proper “species” by careful examination and measurement. Mr. Oldfield Thomas, of the Natural History Museum, has made a special study of them. To give an idea of his work, it may be mentioned that ninety different names had been given by previous writers to as many apparently distinct kinds of rat occurring in India. But by careful measurement and study of the relations to one another of these rats, Mr. Thomas has reduced the number of really distinct Indian species of rats and mice (for a mouse is only a smaller rat) to nineteen. What we call in English water-rats, or water-voles, field-voles, and such little foreign beasts as the lemming and the hamster, are very close to rats in appearance, but are separated on account of clear differences of structure from true rats and mice.