PREFACE TO THE TENTH EDITION 



THE current tendency of physiological thought is clearly toward 

 an increasing emphasis upon the unity of operation of the Human 

 Body. Although the only feasible method of presentation of the 

 subject continues to be by successive consideration of physiological 

 systems one after another, physiologists recognize the desirability 

 of keeping constantly before the mind of the student the fact that 

 in reality the .Body is more than an aggregate of systems: that 

 it is an integer of parts so closely interdependent that the activity 

 of any one calls forth related activities of the others. In the present 

 revision the attempt has been made to keep this idea in the fore- 

 ground. Increased emphasis is placed upon the manifestations 

 of adaptation in the Body; cross references are freely used through- 

 out. As a further assistance toward this end a changed method of 

 treating the subject of chemical co-ordination is adopted. Instead 

 of a chapter, or part of a chapter, devoted to internal secretions, 

 the conception of chemical co-ordination is introduced, concur- 

 rently with that of nervous co-ordination, in an early chapter, 

 and the various hormones are described in connection with the 

 bodily processes they are known to modify. 



Numerous minor changes have been made to bring the pre- 

 sentation abreast of present physiological knowledge. The fol- 

 lowing more or less extensive additions to the subject-matter of 

 the former edition have also been included. A section on the 

 physical chemistry of the Body is added to the first chapter. To 

 this the paragraphs on filtration, osmosis, and dialysis are trans- 

 ferred from the chapter on blood in which they were formerly 

 given. A brief discussion of crystalloids, colloids, solutions, and 

 the significance of cell membranes is also included. The concep- 

 tion of the Body as a machine in its energy relationships, obeying 

 the familiar laws of mechanics, is emphasized more strongly than 

 hitherto. In connection with the discussion of muscle physiology 

 a rather full account of the energy transformations in active muscle 

 is given. The section on the nervous system has been modified 



