PREFACE. 



IN this edition the same method is adopted as was followed 

 in the former edition, entitled " Practical Physiological 

 Chemistry," but further experience in teaching has led me 

 to believe that the book would be improved and made more 

 useful if its scope were extended. New sections upon organic 

 chemistry and organic substances found in plants, together 

 with methods used in more advanced work, are therefore in- 

 cluded. 



As the basis of the book is Organic Chemistry this term 

 is used in its title, and since the subject is also treated from 

 the botanical side, the term Bio-Chemistry is substituted for 

 Physiological Chemistry, a term too often restricted to the aspect 

 of the animal side of the subject. 



The book is still intended mainly for medical students, but 

 it contains the essentials for all students of Biology. The 

 medical student will gain rather than lose by having additional 

 matter, though it may not be of immediate use to him. A 

 survey of the sections upon plant compounds should give him 

 a wider outlook and a deeper insight into the wonderful sub- 

 stances connected with the phenomena of Life, and withal, 

 they may be useful for reference. 



In order to help the student in using the book the essentials 

 of the subject are printed in large type, while the botanical and 

 more advanced portions are printed in small type. The more 

 important practical experiments suitable for a preliminary course 

 are indicated by asterisks and correspond to the small type of 

 the former edition. 



I am much indebted to Dr. C. Lovatt Evans for his 

 assistance in the sections on " The Function of Haemoglobin " 

 and "The Analysis of Blood Gases". Mr. W. W. Reeve, 

 B.Sc., has kindly assisted me with the proofs. 



R. H. A. P. 



