THE FRONTIERS OF MEDICINE 



which frequently manifest their first serious effects on the 

 human being by producing changes in the tissue of the 

 liver and correspondingly prompt changes in the blood. 

 Scientific investigators study these problems not only by 

 chemical and physical studies of the human body, of the 

 blood, and other fluids, but also by careful examination 

 of the organs after death in cases in which fatalities have 

 resulted from poisoning. In such instances the use of the 

 microscope may show great changes in the blood cells 

 that pass through the liver. The very tissue of the liver 

 itself may have disappeared and have been substituted by 

 fat. The metallic substances may be found in the cells 

 of the organ itself. As a result of these studies, it becomes 

 possible to plan methods of treatment that serve to relieve 

 the symptoms, to save lives, and to extend the advance of 

 knowledge still further into the realm of the unknown. 



Metabolism. Before the coming of the modern era, the 

 physician had no way of knowing exactly how well the 

 vital organs of his patient actually were functioning. 

 When it began to be realized that the body is a great 

 physiochemical mechanism in which all sorts of reactions 

 are going on, means were developed for measuring the 

 rate of speed of these reactions and their functional effi- 

 ciency. Everything that takes place in the human body is, 

 to some extent, the result of a chemical change. Whenever 

 any organ performs its duties, energy is used and is trans- 

 formed into some equivalent of a different character. 

 Energy comes from food. When the food is taken into the 

 body, it is broken up into fundamental constituents which 

 are taken up by various organs and transformed into com- 

 pounds which the body can use. The sum of all these activi- 

 ties is the basal metabolism, which is influenced by many 

 factors. 



Formerly the value of all foods was expressed wholly as 

 energy value, or caloric value. It was calculated that one 



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