^\GAi 



X 



FOREWORD 



To the older biologist, microchemistn.- meant the application of 

 appropriate reagents to sections of tissue or to intact cells to enable 

 him to recognize mider the microscope the nature and localization 

 of compounds in li^-ing substance. To the chemist, on the other hand, 

 it signifies the application of instruments of great precision and 

 rigorous methods to the accurate determination of the composition 

 of extremely small amounts of material. To the modem biologist, 

 it includes all of those methods which may aid him to delineate in 

 the exiguous confines of the cell that elusive and mysterious 

 chemical pattern which is the basis of life. To the extent that it 

 requires isolation and purification of compounds, microchemistn.* is 

 but a significant extension of the usual methods of biochemistry-, 

 but with the discovery- of methods of isolating microscopic and 

 submicroscopic and even ultramicroscopic components of lining 

 substance, and the application of physical and chemical methods of 

 analysis to them, the new microchemistrf promises to become the 

 most important tool we possess for elucidation of the fundamental 

 chemical pattern of protoplasm. 



In our enthusiasm for these methods, however, we must not forget 

 that by far the most sensitive instrument for microchemical analysis 

 is the li\'ing organism itself. The methods of immunology*, for 

 example, suffice to discriminate between compounds so closely 

 related that the chemist is at a loss to distinguish between them. 

 The genes revealed by genetic experiment exceed by an infinite 

 multiple the meager number of nucleoproteins revealed by bio- 

 chemical research. The bioassay methods depend on the exquisite 

 sensiti\'ity of the li^-ing organism to minute changes in its chemical 

 en\-ironment. These are also microchemical methods. 



In this volume, the author has chosen to follow the historical 

 pattern and to present the methods of microscopical analysis first. 

 In this field, the difficulty is not so much to find suitable reagents 

 as to prepare material in a form susceptible to microscopic study. 

 Botanical material for a long time possessed definite advantages, 

 since the support aft'orded by cellulose walls, and. in higher plants, 



