1 198 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



after a heavy meal." In more recent studies the hypo- 

 thalamus rather than the bulb has become the locus 

 of the hypothetical actions by the blood, although 

 Larsson (54) noted feeding after stimulation of the 

 region of the dorsal motor nucleus of the vagus. Some 

 of the most lively controversy in this field has arisen 

 from attempts to identify the 'conditions of the blood' 

 to which the hypothalamus responds. Meanwhile, 

 Sherrington's question of whether changes in the 

 blood can actually initiate nerve impulses remains 

 unanswered. 



There is now a tendency to use a measurement 

 of food intake or water consumption as a criterion 

 of the presence of hunger or thirst, in order to a\oid 

 the uncertainties of sensation. Data can be obtained 

 which are fairly precise and al.so reproducible. This 

 approach seems to be at least a modest step forward 

 since only a few years ago these quantities were re- 

 garded as so unpredictable that their regulation was 

 little studied. Credit for remedying this situation 

 belongs in larger part to Gasnier & Mayer (35) and 

 to Adolph (i, 2) who showed that food and water, 

 respectively, can be treated in a quantitative fashion. 

 Adolph's monograph encouraged other investigators 

 to try to discover some of the causes of the apparent 

 unpredictability in these regulations, and to endeavor 

 to identify the regulating mechanisms. Fifteen years 

 ago most animal rooms were not air conditioned so 

 that fluctuations in environmental temperature af- 

 fected feeding; the influence of the estral cycle was 

 suspected but not established (21, 78); and the effects 

 of changes in composition of the diet were almost 

 unstudied from the point of view of their effect upon 

 food and water intake (3, 84). When these and a rela- 

 tively few other factors are controlled, a record of 

 either food or water intake is a reliable guide to ap- 

 petite or thirst if these phenomena are defined simply 

 as desire for food or water. It is possible to measure 

 also the rate of eating, frequency of meals and in- 

 tervals between them (12). Experiments have been 

 carried out upon normal animals in different en- 

 vironmental and metabolic conditions, upon animals 

 with operations upon the nervous system and upon 

 animals having electrodes or hollow tubes implanted 

 in the brain for study after recovery from the effects 

 of anesthesia. 



Most of the experiments on the nervous system have 

 been done to measure total food or total water intake 

 in animals fed standard diets. They offer little under- 

 standing as to just how hunger differs from thirst 

 except that one is a response to deprivation of food, 

 the other to lack of water. We know only from per- 



sonal experience that one seems referred to the epi- 

 gastrium and the other to the mouth and pharvnx. 

 Animals do not always distinguish between the two 

 states; thus, a newborn mammal obtains water and 

 food simultaneously in the mother's milk and, pre- 

 sumably, has no need for separation of hunger and 

 thirst. The capacity to discriminate between the two 

 appears in infancy, since Cooke found evidence of it 

 in babies of 3 mos. and older (27). Even more com- 

 plex and uncertain is the ability of animals to make 

 a selection among diets of distinctive composition 

 (74> 75) snd among the "specific" hungers, of which 

 salt hunger is believed to be a prominent example. 

 How the body 'knows' that it needs protein rather 

 than carbohydrate, carbohydrate rather than fat, 

 a diet containing a particular vitamin or amino acid 

 rather than a deficient diet, or, for that matter, food 

 rather than flavored sawdust, is a mystery. 



BEH.WIOR, COMP.\R.\TIVE ETHOLOGY .A.ND PSYCHOLOGY 



Both feeding and drinking require behavior inove- 

 inents more complex than those of simple reflexes. 

 If all of the data relating to feeding behavior of higher 

 animals (including the traditions of animal hus- 

 bandry), and all psychological studies where hunger, 

 appetite, satiety or thirst are important variables 

 were to be reviewed, the result would be a large en- 

 cyclopedia. Included would be not only food ac- 

 ceptance, but searching, recognition and discrimina- 

 tion, in addition to practically innumerable studies of 

 motivation and aggression, as well as the problems 

 of innate behavior, instinct, learning, memory, con- 

 ditioning habit and prejudice (14, 44, 79, 87). In 

 brief, if feeding and drinking could be explained, 

 some of the most important questions in neurophys- 

 iology and psychology could be answered at once. 

 The present review is incomplete in that it does not 

 explore the neurological basis of nursing, chewing, 

 swallowing, nor processes concerned with rumina- 

 tion and other similar activities; it gives slight atten- 

 tion to grazing, pursuit, fighting, hoarding and ma- 

 ternal behavior in feeding the young; it hesitates to 

 mention the possibility that even the most complicated 

 of activities, man's labors, trades, professions and 

 even wars have reference in some way or other to 

 urges to eat and drink. Food is, without any doubt, 

 the oldest and most widely used 'tranquillizer.' This 

 subject is no small one; adequate study will provide 

 a tremendous quantity of interesting and important 

 data. 



