Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. The changes introduced into this Edition are slight, and only of such a character as to bring the work up to date. The principal subject which has come to the front since the first edition was written is the standardisation of disinfectants, and on this I have added a few paragraphs. I have also endeavoured to simplify the directions.