NUTRITIVE VALUE OF FISH AND SHELLFISH 503 



At some stage in the development of man he found that little effort 

 was required to secure essential foods by domesticating animals and 

 allowing them to gather and eat the grass, grain, etc. They trans- 

 formed these raw materials into meat, milk, dairy products, and 

 eggs. It is clear that the food fishes are doing likewise in the sea, 

 lakes, and rivers. 



It is not the purpose of this chapter to discuss anything more than 

 the general composition of fish and shellfish from the nutrition stand- 

 point. Other fascinating subjects, such as the role of iodine in fish, 

 the wonderful power of certain fishes to store vitaxnins, as in the 

 case of the liver oil of certain fishes, and the occurrence of unusual 

 elements and metallic derivatives in these foods will be discussed in 

 separate chapters. The storing of certain essential amino acids in 

 the protein of the muscles of fishes will also be discussed later. 



THE HUMAN BODY— A PERFECT TRANSFORMER OF ENERGY 



Like every other engine or motor that depends upon heat for its 

 power, our bodies can only transform as much energy as is made 

 available to them. In other words, the human body can not create 

 energy; it can only change the stored energy existing in the foods 

 that we eat into heat to keep the body always at its temperature of 

 98.6° F. and to supply it with the energy necessary for the work 

 which it performs. In addition, our foods must replace the materials 

 utilized and destroyed in the body cells during their life activities. 



This time-worn figure of speech — comparing the human body to 

 an engine or motor — is only a very crude simile. As a matter of 

 fact, the efficiency of the human body in converting food (fuel) into 

 heat and work is almost 100 per cent, while that of the most higUy 

 developed internal-combustion engine or mercury-vapor power plant 

 is very much less. Furthermore, the human body is a self-sustaining 

 and regulating mechanism unlike any machine ever devised by man. 

 It builds itself up out of the foods which we eat; it maintains itself 

 in the same way and makes good its losses; it provides its own lubri- 

 cation, eliminates all of its waste products, and regulates its own 

 body processes to suit the needs of the occasion. In other words, it is 

 a most wonderful transformer of energy. 



As has been stated, the real source of energy in our foods is ulti- 

 mately the sun; so our bodies are at aU times actually utilizing for 

 various purposes the stored-up energy of the sun, just as our steam- 

 power generating plants and internal-combustion engines are trans- 

 forming into useful work the solar energy fixed ages ago in the form 

 of coal and petroleum. 



Just as the engineer can estimate the amount of energy available 

 in different kinds of fuel for purposes of producing power, so can we 

 determine, by proper apparatus, the fuel value of foods. A conuoaon 

 unit for these energy measurements is the "calorie." Speaking in 

 terms of the everyday units of measurement, a calorie is the amount 

 of heat necessary to raise the temperature of 1 pound of water 4° 

 F. ; or, stating it another way, 1 pound of starch, if completely burned 

 to produce heat and energy either outside the human body or within 

 it, wiU develop enough heat to raise 1,900 pounds of water 4° F. in 

 temperature or to raise about 5 gallons of water from the freezing 

 point just to the boiling point. 



