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A TEXTBOOK OF PHYSIOLOGY 



period taken to double their -weight at birth, it appears that in all 

 such animals, except man, there is a law of constant energy consump- 

 tion, the total amount of energy necessary to form 1 kilogramme of 

 animal weight being the same for all animals 4,808 calories of food. 

 Man requires about six times this amount. 



Secondly, in such animals the same fractional part of the food 

 energy taken in is used for growth the " growth-quotient " being 

 34 per cent. 34 calories of each 100 calories of food being used for 

 growth. In man, the growth quotient is but 5 per cent., being greatest 

 at birth, and sinking slowly to zero at maturity, when food is used 

 only for metabolic, and not for growth purposes. 



In regard, also, to the amount of energy for each kilogramme of 

 body weight during the period of life from maturity to death (a period 

 of sixty years twenty to eighty), a calculation showed that each 

 human kilogramme requires 725,770 calories, the other animals 



Fu. 460. TISSUES OF FLAT-WORM, SHOWING AMITOTIC DIVISION CF NUCLEUS. 

 (After Child, from Pahlgren and Kepner.) 



mentioned but 191,600 calories. What exactly determines this power 

 of assimilation it is difficult to say. If it be, as is suggested, a matter 

 of certain chemical complexes, it is obvious that these complexes in 

 the human cells can perform the transformations and changes for a 

 greater number of times than can the cells of other animals ere they 

 expire. 



Cell Reproduction. The division of the nucleus precedes that of the 

 cell. Separated from its nucleus, a cell is unable to grow and divide. 

 The division of the nucleus and of the cell may be relatively simple, 

 known as amitosis or of complex nature, known as mitosis, or 

 karyokinesis. 



In the first process, amitosis, the cell divides somewhat in the 

 following manner : At first, the nucleolus elongates at right angles to the 

 plane in which division will subsequently take place. It then divides, 

 and the two daughter nucleoli pass apart to what will be the centre 

 of the new daughter cells. Next, the nucleus divides rarely by a 



