PREFACE TO THE FOURTH EDITION. Xlll 



Dr. Hutchison's inquiries on the movements of Respiration ; to the 

 second, the data furnished by the researches of MM. Regnault and 

 Reiset, Prof. Scharling, M. Barral, and others, upon the amount of 

 Oxygen absorbed and of Carbonic Acid exhaled ; whilst the third, in 

 which the "Effects of Suspension or Deficiency of Respiration" are 

 discussed, has been largely augmented by a summary of the evidence 

 afforded, by our recent experience, of the marked tendency of an habitu- 

 ally imperfect Respiration to produce a liability to Zymotic disease. 

 Nearly the whole of Chapter xi., ".On Nutrition," has been newly 

 written for this Edition ; and here, as elsewhere, the Author has been 

 greatly indebted to the Hunterian Lectures of his friend, Mr. Paget, 

 whose contributions to this department of Physiology he regards as of 

 the highest scientific as well as practical value. He cannot forbear, 

 moreover, to express the pleasure which he has derived, from finding 

 that Mr. -Paget most fully recognizes, and gives him credit for two im- 

 portant doctrines which he had taught in former editions of this work ; 

 namely, the limits to the Duration of individual parts, imposed by the 

 very fact of their independent vitality, and varying with the activity, of 

 their vital operations ; and the diminished formative power of the tissues, 

 as one of the essential constituents of the state of Inflammation. In 

 Chapter xn., "On Secretion and Excretion," important additions have 

 been made under almost every head ; and those parts, especially, which 

 relate to the agency of the Excretory apparatus in maintaining the 

 purity of the Blood, have been extended. This Chapter, however, is 

 less comprehensive than formerly ; several of the subjects which it pre- 

 viously included, having been transferred to portions of the work in 

 which they seemed to find more appropriate places ; the Salivary and 

 Pancreatic secretions being now treated of in the Chapter on Digestion, 

 and those of the Testes and Mammae in that on Generation. Of the 

 three subjects included in Chapter xin., " On the Evolution of Heat, 

 Light, and Electricity," the first alone had been systematically con- 

 sidered in the previous editions, and this has been considerably ex- 

 tended in the present ; under the second head will be found some very 

 curious observations on the evolution of Light in the living Human 

 subject ; and under the third is given a summary of the results of the 

 admirable researches of M. Du Bois-Reymond, which have been recently 

 brought before the scientific public in this country by Dr. Bence Jones. 

 It is in the Chapter (xiv.) devoted to the Functions of the Nervous 

 System, which constitutes one-fifth of the entire volume, that the great- 

 est additions and alterations will be found. This subject, in its Psycho- 

 logical as well as in its Physiological relations, has occupied more of the 

 Author's attention than any other department of Physiology ; and he 



