REGULATION OF FEEDING AND DRINKING 



1203 



subject here, since it is the author's behel that a 

 variety of factors is important and that it is not pos- 

 sible at tlie present time to assess quantitatively the 

 relative significance of each. 



SUPPLEMENTARY MECHANISMS 



Presenting these generalized changes that could 

 act upon the hypothalamus should not lead to a 

 neglect of more definite, although possibly more 

 limited, sensory mechanisms. The ability of the 

 month, pharynx and upper esophagus to 'meter' both 

 water and food is well established (i, 16, 17, 47, 

 52, 88), and so is the inhibiting effect of gastric dis- 

 tention (4, 47, 89). The sensation of hunger arising 

 in the stomach, and of thirst referred to the mouth 

 and pharynx, are powerful reminders of a need for 

 food or water. Yet the disappearance of gastric hunger 

 as fasting is prolonged, its absence during cold ex- 

 posure (26), the normal feeding responses of animals 

 without innervation of the gastrointestinal tract 

 (41, 42) and the persistence of appetite after removal 

 of most or all of the stomach (92), all indicate that 

 either generalized or central perception is more 

 critical than the localized one in achieving the overall 

 regulation (13, 66). One may suppose, as Carlson 

 did, that a newborn baby cries when its empty 

 stomach contracts, that filling the stomach with milk 

 inhibits the contractions and that this sets up a 

 learned response where feeding is associated with 

 relief of gastric pain (26). However, very young babies 

 (just how young is uncertain) can be fed at intervals 

 throughout the day with no periods of crying and no 

 evident gastric distress (personal observation). They 

 evidently experience a cycle of appetite-satiety- 

 appetite, etc., without definite pain. Adult subjects 

 sometimes report the same experience (60), as a well- 

 known child psychiatrist assured this reviewer that 

 gastric pains as an accompaniment of the hunger 

 state were completely unknown to him. 



The diagram of figure i presents a simplified out- 

 line of a multifactor concept of regulation of feeding, 

 based on the conclusions that appetite is converted 

 into satiety by the processes of eating and filling the 

 stomach, by relief of hypoglycemia or inadequate 

 supply of glucose, and by shifting of body water, as 

 well as by the thermal stress of the S.D.A. This dia- 

 gram may be incomplete since other reactions may 

 remain now unknown. Its principal value is that it 

 illustrates the ability of the central nervous .system 

 to take manv different kinds of change within the 



APPETITE 



i 

 FEEDING 



J 



Relief of 

 hypoglycemia 



\ . 



S.D.A. 



Rising 

 heat load 



SATIETY 



FIG. I. .Simplifieid outline of a multifactoi' concept of the 

 regulation of feeding. 



body and integrate them into a pattern of activity 

 or response. Whether all of these factors act upon the 

 hypothalamus is not known; but all of them must act 

 eventually upon feeding reflexes, which means that 

 they must either directly or through other neural 

 pathways affect the motor nerve nuclei of the brain 

 stem. One can understand how the three generalized 

 changes — glucose lack, water movement and thermal 

 gradients — might act upon the same neuron or upon 

 all neurons. Wherever their critical actions, the end 

 result of a deficiency of food must be active facilitation 

 of reflexes necessary for feeding, as a lack of water in 

 a similar fashion must facilitate drinking refle.xes. The 

 key reactions within the brain are facilitation and 

 inhibition, applied discretely enough to allow animals 

 to distinguish between need for food and for water 

 and to provide a basis for specific hungers or appe- 

 tites. That is, facilitation and inhibition must be 

 selective. This implies a type of discrimination within 

 the tegmentum or in mechanisms closely related to it 

 and calls to mind .Sherrington's conclusion that there 

 is a spinal hunger state (77). He noted (p. 845), "As 

 a broad rule, spinal reflexes are more easily elicited 

 when a well-nourished animal is hungry and expect- 

 ing food, and less easily when it has just heavily fed. 

 There is, so to say, a spinal hunger." 



In writing about thirst^, authors seem inclined to 

 follow the pattern already outlined for hunger and 

 appetite. Andersson (9), Andersson & McCann (10, 

 11) and Greer (39) have all observed drinking to 

 follow perfusion or stimulation of the hypothalamus. 



^ Wolf has recently published a monograph on thirst that is 

 both informative and interesting, and has immediately become 

 the classic discussion of this subject (93). 



