ESSENTIALS 



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CHEMICAL PHYSIOLOGY 



INTEODUCTION 



Chemical Physiology or Physiological Chemistry, as it is some- 

 times termed, deals with the chemical composition of the body and 

 with the chemical changes it undergoes ; it deals also with the com- 

 position 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 an}-thing positive about the chemical structure of living matter, 

 because the reagents he uses wiU destroy the hfe of the tissue he 

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

 examines non-Uving 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 ceUs becoming grouped in different 

 ways, by alterations 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 hnings; in others the 



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