

INTRODUCTION. 



MY colleague's book, in its earlier editions, received so hearty and 

 so general a welcome that any personal words of recommendation 

 seem now uncalled for. In this edition, however, it emerges as 

 a work of a somewhat different order. 



Like all good books which deal with a progressive subject, it 

 has felt the growth impulse, and, notwithstanding the exceptional 

 nature of the times, material for growth has during the last few 

 years accumulated in abundance. If this edition has largely out- 

 grown its predecessors the increase is not only desirable, but, in 

 my opinion, necessary. 



Progress in any science calls continuously for new methods, 

 and for extension and improvement in technique. In the growth 

 of any branch of knowledge there are, indeed, periods when the 

 development of technique becomes the most pressing of needs, and 

 its success the best measure of progress. Biochemistry has been 

 successfully passing through such a period. Its methods have 

 been greatly multiplied, extended and improved. We are now 

 beginning to reap the reward in the accumulation of accurate 

 quantitative data. One need peculiar to biochemistry, that of 

 following changes in living tissues without terminating the life of 

 the animal, or harming the human subject, has now been largely 

 met, at least so far as studies of the blood are concerned. This is 

 due to the success of micro-methods of analysis. So significant are 

 some of the results which can be obtained that we may hope to see 

 the methods become as general in connexion with medical diagnosis 

 as the use of the stethoscope or the electrocardiogram. 



It may be good for the advanced student, possessed of leisure, 

 to determine for himself the exact conditions necessary for success 

 in the use of a given method. For two classes, however, it is highly 

 desirable that success should be reached as immediately as possible : 

 for the elementary student, in order that his faith may not be 

 weakened, and for the research worker not specially versed in 

 chemical technique, who, with limited time, wishes to apply a 

 method to medical or biological problems. Each of these will be 



