A major feature of this revision is the greater depth to which many of the fundamental aspects of pharmaceutics have been treated. This has necessitated deletions elsewhere: including the section on the history of pharmacy. because several textbooks on this subject are available; the chapter on surgical dressings. because much of the information that was included previously is more appropriately taught in pharmacognosy; the detailed descriptions of the preparation of products from vegetable sources. because. today. these have little relevance in most fields of pharmaceutical practice; and the discussion of endocrine glands and hormones. a large part of which is covered in physiology courses. A further important change is the introduction of the International System of Units (SI units). This has presented a number of difficulties (see Chapter 1) and was further complicated by the fact that even experienced supporters of the scheme do not always agree on the interpretation of some of the recommendations. In consequence. one or two of our decisions may appear debatable; nevertheless. there is no doubt that. as the system has been adopted throughout most of the world. pharmacy students should be using it now.