MODIFICATION IN GROWTH 179 



millimeter has been determined for each sex, table 122 — at a series 

 of selected body lengths; values for intervening lengths may be 

 had by interpolation. After 60 mm. in body length the ratio for 

 the female is higher than that for the male. By the use of this 

 table it can be determined whether a given rat is emaciated or 

 fat. 



5. Modifications of growth in total body weight and organs. 

 The foregoing data on growth on age represent the usual results 

 under moderately favorable conditions. By improvement in 

 the food and other conditions, more rapid and greater final growth 

 can be obtained (Greenman and Duhring, '23) . Most investigators 

 at the present time carry a series of litter controls with which 

 their test rats are compared, and this should be done wherever 

 possible. It is to be kept in mind that the usual results run 

 much closer to the maximum than to the minimum, i. e., it is 

 much easier to retard and reduce the growth of the rat than it 

 is to accelerate or increase it. Thus, in a sense, slight gains 

 are equivalent to large losses. 



Body growth is better after lecithin feeding (Hatai, '03 a) 

 and with various forms of abundant and varied diets. Increased 

 growth occurs in spayed females (Stotsenburg, '13) due in part 

 to the formation of fat. 



Bearmg young increases the body weight of the female (J. B. 

 Watson, '05). Some young, undersized at birth, also grow more 

 rapidly than their litter mates (King, '16). Exercise improves 

 growth (Donaldson 'MS.). 



Body growth is poorer under starvation conditions and with 

 all forms of defective, deficient or monotonous diets. Isolated 

 animals grow less well than those kept together. Disturbed 

 surroundings, visitors or change of the caretaker cause arrests 

 in growth or even losses in weight. 



The effect on body growth of the removal of the thyroid and 

 parathyroid glands (Hammett, '23) is given on page 162. 



Body growth is not affected by castration (Stotsenburg, '09) 

 nor by either single or double "isolation" of the ovaries within the 

 rat, despite the fact that in double isolation the ovaries are much 



