So short a time has elapsed since the appearance of the second edition of this little book that many changes have not been neces sary. The title has been somewhat modified to suit the changes made. A number of new subjects have been introduced, and at the request of many using the work the cuts have been bound with the text. The author has freely consulted standard works and journals upon the various subjects discussed. Thanks are 'due the editors of medical and scientific journals for the words of encouragement and suggestions of value, which the author has gladly received. Especial thanks are due Prof. J. B. Marvin, of Louisville, who has kindly gone over the entire text and given the author valuable aid.