ESSENTIALS 



OF 



CHEMICAL PHYSIOLOGY 



INTRODUCTION 



Chemical Physiology or Physiological Chemistry deals with the 

 chemical composition of the body and with the chemical changes it 

 undergoes ; it also deals with the composition of the food which 

 enters, and the excretions which leave, the body. 



When a chemist examines living things he is placed at a dis- 

 advantage when compared with an anatomist; for the latter can 

 with the microscope examine cells, organisms, and structures in the 

 living condition. The chemist, on the other hand, cannot at present 

 state anything positive about the chemical structure of living matter, 

 because the reagents he uses will destroy the life of the tissue he 

 is examining. There is, however, no such disadvantage when he 

 examines non-living matter, like food and urine, and it is therefore 

 in the analysis of such substances that chemical physiology has 

 made very important advances, and the knowledge so obtained is 

 of the greatest practical interest to the student and practitioner of 

 medicine. 



The animal organism is in its earliest embryonic state a single 

 cell; as development progresses it becomes an adherent mass of 

 simple cells. In the later stages various tissues become differen- 

 tiated from each other by the cells becoming grouped in different 

 ways by alteration in the shape of the cells, by deposition of inter- 

 cellular matter between the cells, and by chemical changes in the 

 living matter of the cells themselves. Thus in some situations the 

 cells are grouped into the various epithelial linings; in others the 



B 



