REGULATION OF FEEDING AND DRINKING 



I 199 



SIGNIFICANCE OF NERVOUS SYSTEM 



Two of the more enlightening discussions of hunger 

 and appetite, those of Carlson (26) and of Adolph 

 (3), begin and conclude, respectively, with the idea 

 that feeding is an activity of all animals, including 

 those having no ceiitral nervous system. Adolph wrote 

 (p. 124): "All animals that have been studied, those 

 without alimentary tracts as well as those which have, 

 recognize food, spurn food when it is superabundant, 

 and put forth extra efforts to get it when it is rare. 

 Hence, whatever be the machinery that may fi.x the 

 pattern of priorities in rats, comparable patterns seem 

 to be endowments of all animals, whether or not they 

 possess specialized neuromuscular or alimentary 

 systems." It seems possible that study of these phe- 

 nomena in higher animals might progress more 

 quickly if more were known about the liehavior of 

 lower forms, including those possessing no central 

 nervous system. 



The relative significance of a given portion of the 

 nervous .system, for example, the hypothalamus, may 

 be evaluated by asking which animals have this part 

 of the brain. According to Ca'osby & VVoodburn (29) 

 the hypothalamus is well developed even in cyclo- 

 stomes. [Insects and other arthropods have ganglia 

 that may serve some of these same functions.-] 

 One cannot say whether the development of this part 

 of the brain is to be regarded as advanced in lower 

 animals or as primitive in man. The fact that it is 

 similar throughout the series of vertebrates suggests 

 that it serves activities common to all of them and 

 leads to a desire for more information on feeding 

 mechanisms and behavior from the point of view of 

 comparative physiology. 



In contrast to the relative simplicity of the hypo- 

 thalamus and its uniformity among vertebrates are 

 the specialization and complexity of higher parts of 

 the brain. As in other forms of behavior, the functions 

 of the cerebral cortex in feeding are probably more 

 evident in man than in lower animals, yet in man they 

 are most difficult to analyze. Basic mechanisms seem 

 often to be obscured by habits, customs and preju- 

 dices that a physiologist has no way to study. Perhaps 



^ In addition to earlier papers by Dethier (31), a more re- 

 cent account of his experiments reveals that in blowflies feeding 

 on sugar solutions, two mechanisms are important. One is the 

 taste of the solution; the other is the degree of distension of a 

 certain part of the foregut. On the basis of these two mecha- 

 nisms Dethier & Bodenstein have explained the quantitative 

 features of feeding activity in flies (30a). They are the first 

 authors to have achieved this goal using any animal. 



the adult human brain should be put aside for the 

 moment in order to study the nervous system of 

 babies which is simpler in both organization and 

 function. In a baby nursed only by his mother, the 

 regulation of feeding and drinking is probably as 

 straightforward as it can be in a human situation (27). 

 The behavioral responses of babies include the sleep- 

 ing-waking cycle, crying, general movements of body 

 and extremities, and basic feeding reflexes allowing 

 them to locate the nipple, grasp it, suckle and swallow. 

 They definitely exhibit appetite and satiety. The 

 regulating system, of course, includes the mother, 

 since the amount of milk the baby gets is a function 

 of the rate of milk production, amount stored in the 

 breast, and activity and duration of activity of 

 mechanisms making it available to the baby, e.g. 

 milk ejection. That these are present in other mam- 

 mals may encourage a comparative study. These 

 advantages seem so obvious that one asks why more 

 studies have not been done. There are at least two 

 reasons: pediatricians in hospitals usually do not have 

 the baby's mother present to complete the regulating 

 system; and physiologists observing a baby in their 

 own family .sometimes have difficulty in remaining 

 objective about the situation. When, rarely, a first- 

 hand report does appear, it may have the interest 

 and clarity of the papers by the Newtons (68, 69); 

 they studied, however, the maternal side of the 

 regulating system. To encourage further research an 

 environment like the one said to exist in nursing 

 homes in England seems to be desirable. There an 

 experienced mother nursing at least her second child, 

 free trom cares of the rest of the familv for possibly 

 3 weeks, could provide data to answer many ques- 

 tions. Related experiments, of course, can be and have 

 been performed in laboratories and at agricultural 

 experiment stations; but their goal has been, .so far 

 as I can learn, to discover how to make the offspring 

 grow the most rapidly or how to obtain a maximal 

 milk production. The same techniques should be 

 suitable for studying, rather, the organization of the 

 regulating svstems. 



INTERRELATIONSHIPS AND INTEGRATIONS 



Regulation of food and water intake are examples 

 of the integrative activity of the nervous system — 

 integrations more complex than those of the reflexes 

 in Sherrington's classic inonograph. VV'hen the inte- 

 gration is considered only in a quantitative sense of 

 how much food or water is taken, the part of the 



