REGULATION OF FOOD AND WATER INTAKE 



35; 



longest time. It includes records daily of body weight, food intake, number 

 of self loads, and total number of responses (bar presses). 



Note first that the transition from oral to intragastric ingestion is made 

 with ease. Two indices of regulation were used. First, decreasing the 

 concentration of the diet to 50 per cent by dilution with water resulted in a 

 prompt and sustained doubhng of intake, number of self loads, and number 

 of responses. The adjustment downward when the diet was returned to 

 full strength, was equally precise. 



ORAL 



X ^330+ 



v^-^60- 

 ^^ 20+ 



^^ 50" 

 ^< 30" 



g2 10:: 



900-h 

 \^ 700f 



z 



2 500+ 



CO 



LU 



^ 300 



100 



INTRAGASTRIC 



Lil 



u 



J_l 



1 1 1 1 1 1 



50% 

 Dilu- 



u 



U 



LLi 



iiJ 



Second 

 25:l2i5d25! 



ILi 



15 



iiiiiii 



ii . ii 1 1 1 



FR-6- 



FR-36 



20 



5 10 



DAYS 



Fig. 4. Body weight, daily food intake, the number of self-loads, and the 

 number of daily responses during 3 days of oral food intake and 25 days of 

 intragastric intake in the normal rat. (From Epstein and Teitelbaum, 1962b.) 



Second, food intake and body weight were regulated with comparable 

 precision in the face of sudden halving or doubling of the size of the in- 

 dividual stomach loads by appropriate and precise changes in the number of 

 loads taken. While working for a standard load of 2.5 ml on the day before 

 these changes, the animal in Fig. 4 obtained 34 ml of diet by injecting itself 

 15 times. When the size of the load was halved the animal obtained 28 ml 

 in 28 injections, and when the load was doubled the animal obtained 

 33 ml in only 7 injections. In addition, motivation for food was main- 

 tained. Total daily responses rose proportionally as the number of bar 

 presses required to obtain each load was gradually increased from 6 to 36 

 so that intake and body weight remained well within normal Hmits. When 



