NORMAL AND PATHOLOGICAL GROWTH 149 



can be formed and diverted to the blood stream, then the sugar 

 present in the blood is quickly oxidized and disappears and the 

 animal becomes unconscious and dies as before. The truth of 

 these facts is based on numerous experiments in which the arti- 

 ficial supply of pancreatic secretion is furnished, 2 or artificial 

 sugars are injected into the circulation. 3 Either step is promptly 

 followed by temporary recovery and normal behavior. The 

 interdependence of the nervous system, the muscles, the pan- 

 creas and the liver, and other adult organs of the body, largely 

 chemical in the illustration used, is* obviously essential to the 

 continued activity and normal growth of man and mammals. 



The growth-influencing factors include not only that proto- 

 plasmic complex of inheritance which we describe by the phrase 

 "the growth impulse," but they include the physical and chemi- 

 cal processes going on in every individual part of the body at 

 every moment whereby that part exerts directly or indirectly 

 either a stimulating or a restraining influence on other parts 

 of the individual. 



One may summarize for emphasis the general facts de- 

 scribed in this introduction. They are: (1) growth during the 

 life cycle of individual animals proceeds 2 according to a certain 

 mass-time ratio expressed by the curve of growth. (2) Growth 

 of the individual parts of the animal occurs at very decidedly 

 different rates than the average growth as a whole. (3) The 

 maximum rate of growth in different organs is reached at dif- 

 ferent times in the life cycle. (4) Growth rate and growth vol- 

 ume and differentiation within the body are conditioned first of 

 all by the unknown capacity of the protoplasm expressed by the 

 phrase "the growth impulse." These factors are inherent but 

 vary widely in different species. (5) Coincident with the mor- 

 phological differentiation of parts of the body of animals and 

 of man, there is a functional differentiation equally intricate 

 and diverse. (6) It is a law of physiology that the functional 

 act in the tissue or group of tissues stimulates the rate of growth 

 in that tissue. This influence apparently has a chemical or 



