174 ALIMENTATION. 



first had a most voracious appetite ; she never felt satisfied. She continued to eat, even 

 when the first portions of food which she had taken were escaping through the opening. 

 She would then say that she felt better, but was still hungry. Prof. Busch infers that 

 hunger is composed of two separate sensations one general, the other local ; the former 

 resulting from the want of material to supply the waste of tissue." Such facts render 

 it certain that the appetite and the sense of hunger are expressions of a general want on 

 the part of the system, referred by our sensations to the stomach, but really located in 

 the general system. This want can only be completely satisfied by the absorption of 

 digested alimentary matter by the blood and its assimilation by the tissues. 



The sense of hunger is undoubtedly appreciated by the cerebrum, and it has been a 

 question whether there be any special nerves which have the function of conveying this 

 impression to the great nervous centre. The nerve which would naturally be supposed to 

 possess this function is the pneumogastric ; but, notwithstanding certain observations to 

 the contrary, it has been proven that section of both of these nerves by no means abolishes 

 the desire for food. Longet has observed that dogs eat, apparently with satisfaction, 

 after section of the glosso-pharyngeal and lingual nerves. This observer is of the opinion 

 that the sensation of hunger is conveyed to the brain through the sympathetic system. 

 Although there are various considerations which render this somewhat probable, it is 

 not apparent how it could be demonstrated experimentally. It is undoubtedly the sym- 

 pathetic system of nerves which presides specially over nutrition ; and hunger, which 

 depends upon deficiency of nutrition, is certainly not conveyed to the brain by any of the 

 cerebro- spinal nerves. 



Thirst is the special sensation which induces the ingestion of water. In its moderate 

 development, this is usually an indefinite feeling, accompanied with more or less sense 

 of dryness and heat of the throat and fauces, and sometimes, after the ingestion of a 

 quantity of very dry food, by a peculiar sensation referred to the stomach. When the 

 sensation of thirst has become intense, the immediate satisfaction which follows the 

 ingestion of a liquid, particularly water, is very great. Thirst is very much under the 

 influence of habit, some persons experiencing a desire to take liquids only two or three 

 times daily, while others do so much more frequently. The sensation is also sensibly 

 influenced by the condition of the atmosphere, as regards moisture, by exercise, and 

 by other circumstances which influence the discharge of water from the body, particularly 

 by the skin. A copious loss of blood is always followed by great thirst. This we have 

 frequently noticed in the inferior animals. After an operation involving haemorrhage, 

 they nearly always drink with avidity as soon as released. In diseases which are charac- 

 terized by increased discharge of liquids, thirst is generally excessive. 



The demand on the part of the system for water is much more imperative than for 

 solids; in this respect being only second to the demand for oxygen. Animals will live 

 much longer deprived of solid food but allowed to drink freely than if deprived of both 

 food and drink. A man, supplied with dry food but deprived of water, will not survive 

 more than a few days. Water is necessary to the function of nutrition, and acts, more- 

 over, as a solvent in removing from the S3 r stem the products of disassimilation. 



After deprivation of water for a considerable time, the intense thirst becomes most 

 agonizing. The dryness and heat of the throat and fauces are increased and accom- 

 panied by a distressing sense of constriction. A general febrile condition supervenes, the 

 blood is diminished in quantity and becomes thickened, the urine is scanty and scalding, 

 and there seems to be a condition of the principal viscera approaching inflammation. 

 Death takes place in a few days, generally preceded by delirium. 



The sensation of thirst is instinctively referred to the mouth, throat, and fauces; but 

 it is not necessarily appeased by the passage of water over these parts, and it may be 

 effectually relieved by the introduction of water into the system by other channels, as by 

 injecting it into the veins. Bernard has demonstrated, by the following experiment, that 

 water must be absorbed before the demands of the system can be satisfied : He made an 



