vi PREFACE 



easily a knowledge of their physiology ; and physiological chemistry is 

 too closely connected with physiology to be neglected in a text-book. 

 Again, the ordinary text-books on chemistry and physics contain little 

 information in regard to the modern physical chemistry, ionization, dis- 

 sociation, osmotic pressure, etc., all of which have important bearings 

 on modern views in regard to physiological processes. While these 

 subjects are by no means exhaustively considered, they are discussed at 

 some length. Embryology might logically precede the study of physi- 

 ology proper; but the difficulties of this subject are more easily sur- 

 mounted by advanced than by first-year students, and for that reason 

 it is considered last. Demonstrations, recitations, and laboratory work 

 go hand in hand; but laboratory technique is a subject for practical 

 instruction with the aid of special manuals. Descriptions of laboratory 

 manipulations and illustrations of instruments and apparatus, therefore, 

 are omitted. 



I have not thought it desirable to give in extenso minute details of 

 what is called nerve-physiology, and only the general results of such 

 work are presented. Full descriptions of electrical phenomena in nerve 

 and muscle are to be found in laboratory manuals. No considerable 

 account has been taken of mathematical formulae and calculations 

 involved in certain special studies, such as physiological optics and 

 acoustics. This would assume a knowledge of mathematics on the 

 part of the student which usually does not exist. Still, the special senses 

 are considered quite as fully as seems necessary, except for ophthal- 

 mologists and otologists. The same may be said of embryology, a 

 subject too large to be fully presented, except in special treatises. The 

 plan of teaching and the arrangement of subjects do not involve a study 

 of the nervous system in its relations to circulation, respiration, diges- 

 tion and metabolism until the second year. Consideration of these 

 relations is given mainly in the chapters on the nervous system, and 

 they are briefly mentioned in the first part of the work. 



For valuable aid in the important matter of illustration, I am under 

 great obligations to professional friends ; but I alone must be held 

 responsible for the text and for the arrangement of subjects. 



In the matter of illustration a new departure is made which bids 

 fair to revolutionize this important aid to the study of histology. After 

 more than a year of experimentation, it has been found possible to 

 reproduce, by what is known as the three-color process, stained histo- 

 logical objects, at all magnifications used in such work, as they actually 

 appear under the microscope. This had already been done in 1895- 

 1896 by Dr. Edward Learning, who photographed the objects, and Mr. 

 Edward Bierstadt, who made gelatin-prints by the three-color process 



