Disturbances of Growth 



E. V. McCOLLUM 



BALTIMORE 



Our knowledge of nutritional processes is the fruit of human experi- 

 ence clarified by scientific inquiry through experiments on animals. 

 Growth is governed entirely by chemical laws. It represents changes which 

 take place in a heterogeneous system consisting of water, proteins, lipins, 

 inorganic salts, glucose, and at least a few other substances whose natures 

 and functions are not understood. These are arranged in such a manner 

 that they form a system which is self-perpetuating, and capable of in- 

 creasing its mass at the expense of non-living matter which serves as food. 

 It can repair, through the agency of food, the fractions of its structures 

 which are degraded through metabolic processes. These changes involve 

 the liberation of the potential energy of the foodstuffs. The kinetic 

 energy may appear in the form of mechanical work, heat, light or elec- 

 tricity. It is the increase in mass, accompanied by certain specializa- 

 tion of parts, and a progressive modification of structure and change of 

 form, that constitutes growth. 



Every living body and every anatomic unit of living matter requires 

 water, oxygen, certain inorganic elements in the form of appropriate salts, 

 a certain atmospheric pressure, and food. A discussion of disturbances 

 of growth involves a consideration of the effects of improperly constituted 

 food upon the body structures. An understanding of the chemistry of 

 foods is essential to a satisfactory comprehension of nutrition. Unfor- 

 tunately our knowledge in this field is still far from complete, but methods 

 of study have been devised which have thrown much new light on certain 

 aspects of the subject. 



Food, to be .complete for the nutrition of a mammal, must supply 

 proteins of a character to furnish the seventeen or eighteen amino acids 

 which are essential for the construction of body proteins. It must contain 

 satisfactory amounts of nine inorganic elements in appropriate com- 

 binations. These are calcium, magnesium, sodium, potassium, chlorin, 

 phosphorus, iodin, iron and sulphur. All of these except sulphur can be 

 utilized in the form of inorganic salts such as chlorids, phosphates, etc., of 

 the bases. Sulphur must be furnished in the form of the sulphur-contain- 

 ing amino acid cystin. In addition to these, the food must furnish the 



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