EFFECTS OF THIRST.] 



CHEMISTRY. 



35. Effects of Thirst. Many instances prove that 

 hunger can be borne for several days before it causes 

 death. If the fasting person drink water, this time is 

 considerably prolonged. While, on an average, man 

 cannot live longer than a fortnight altogether without 

 food; there was, in 1831, an instance at Toulouse, of a 

 convict who, preferring death by starvation to a public 

 execution, survived for as many as sixty-three days on 

 water alone. 



Similar cases prove^hat it is much more difficult to 

 overcome thirst than huager ; and this is confirmed by 

 daily experience. If it be alleged, on the other hand, 

 that many people drink exceedingly seldom, and that 

 females especially can do without drinking for many days 

 together, neither must we forget that all food, even the 

 driest, contains a great proportionate quantity of water. 



Upon this reception of water into the system all de- 

 pends. The blood and most of the tissues, with all 

 secretions and excretions, contain an abundant quantity 

 of water, as an indispensable condition of their right 

 composition and proper action. 



In the excretions from the skin and lungs, more than 

 one-third of the weight of our food is daily lost in the 

 form of water. To this a considerable quantity of water 

 mu->t be added besides, which is voided in the urine. 



A deficient supply of water is, therefore, very soon 

 felt ; dry lips and cheeks, dryness of the tongue and 

 thru.it, speedily betray the lack of that water of the 

 mucus and saliva which ordinarily keeps the cavity of 

 the month in a moist state. On the increase of thirst, 

 the mil 'us membrane reddens and swells, and, after 

 awhile, the inflamed tongue cleaves to the roof of the 

 mouth, and the glowing breath escapes in sighs ; 

 tho skin burns, because the perspiration continually 

 diminishes ; the urine becomes acid, as it contains the 

 usual salts and less water ; tho slackened muscles move 

 the limbs listlessly, and without power ; mere talking or 

 deglutition becomes an effort ; groaning and quick 

 respirations accelerate the pulse. In the action of the 

 brain and organs of the senses, there is the same irritation 

 as in hunger. Restlessness and despair torment with 

 the continual representation of water and other beverages, 

 which would allay his craving. All liquids sea-water, 

 tincture for the teeth, even his own urine are swallowed, 

 or attempted to be swallowed, by thirst -distracted man, 

 with passionate eagerness. If no relief be given, a violent 

 inflammation of the mouth and throat supervenes, with all 

 the symptoms of an acute fever ; sometimes the inflamma- 

 tion causes even gangrene of the throat, a quick, sighing 

 respiration, and a pulse proportionally more rapid ; a 

 , lolling tongue, a whispering delirium and rage, 

 GUI ling in death, if the sufferer do not expire senseless 

 in a swoon, 



Of FOOD. 36. Definition of Alimentary Principles 

 and Nutriment. From the blood are formed the tissues 

 and the constituents of the secretions ; to the blood the 

 materials of tho tissues return after having undergone a 

 certain degree of decomposition, which renders them 

 unlit for the peculiar functions of the different organs ; 

 and these products of decomposition are abstracted from 

 the blood by the excretory glands, which expel them from 



"ly. 



The excretions diminish the weight of the body, and 

 alter the nutrition of the tissues ; their function depends 

 i thuir composition ; and throughout a great division 

 oi the nerves of our bodies this function consists in sen- 

 sation. The sensitive nerves are the media for the 

 perception of all internal and external impressions. In 

 the brain we become conscious of these impressions. 



Hunger and thirst are the sensations which announce 

 to the brain, through tho medium of the nerves, the im- 

 poverishment of the blood. In popular language, every 

 substance is called a nutriment which is able to quench 

 hunger and thirst. The scientific definition of nutriment 

 results from tho cause of these sensations. Whatever 

 substance possesses the power of restoring to the blood 

 the essential constituents which it has lost, and begins 

 the circulation from the blood through the tissuea, may 

 be considered a nutriment in the widest sense. 



All the aliments which restore to the blood the com- 

 pounds of chlorine, the salts, the fat, and the albumen, 

 satisfy the sensation of hunger ; that of thirst is quenched 

 by the restoration to the blood of the deficient water. 



37. Alimentary Principles. All nutriment is com- 

 posed of certain alimentary principles. Under the latter 

 term we comprehend all those compounds which are 

 either identical with the essential constituents of tho 

 blood, or sufficiently similar to be transformed into 

 them by digestion. Essential constituents of the blood 

 are all those which do not originate from the regressive 

 transformation of the tissues. 



To tliis general definition we have to add, as a special 

 one, the difference between alimentary principles and 

 aliment. By ordinary dissolving media, like water, 

 alcohol, and ether, simple constituents can be separated 

 from the aliments, but not from the alimentary principles. 

 These simpler constituents of the aliments, which cannot 

 be separated by common dissolving media into any fur- 

 ther parts, are the alimentary principles themselves. 



Though the alimentary principles are often denominated 

 the elementary constituents of tho aliments, they are by 

 no means to be confounded with the elements in a che- 

 mical sense. The latter cannot be decomposed into other 

 substances manifesting, abstracted from form and colour, 

 any essential differences ; the alimentary principles can 

 be decomposed, but only by agencies which act more 

 powerfully than simple dissolving media, like water, 

 alcohol, and ether. 



No alimentary principle is composed of fewer than 

 two elements ; the simplest alimentary principles, like 

 water and common salt, arc combinations of two elements. 

 A great many alimentary principles, as fat, sugar, and 

 most of the vegetable acids, contain carbon, hydrogen, 

 and oxygen ; the inorganic salts consist of oxygen com- 

 bined in the basis, and the acid with two different 

 elements. All these alimentary principles are formed of 

 three elements. 



Four elements are found in the soaps which, in addition 

 to the carbon, hydrogen, and oxygen of these fatty acids, 

 contain a metal, forming with oxygen the basis alkali of 

 the soap. 



Finally, those organic alimentary principles, in which 

 nitrogen and sulphur are associated with carbon, hydro- 

 gen, and oxygen, are composed of five elements ; and 

 some others, containing phosphorus, of six. To tho 

 former belongs gelatine ; to the latter, albumen. 



38. Digestive Principles. Before discussing tho pro- 

 cess of digestion, we classified the alimentary principles 

 into inorganic, organic without nitrogen, and organic 

 with nitrogen. 



To the inorganic alimentary principles belong the com- 

 pounds of chlorine, as common salt, and the combinations 

 of inorganic acids and bases, which chemists, abandoning 

 the ordinary use of language, designate by the name of 

 salts. 



The starchy matters and fatty substances, with by 

 far tho greater part of the acids of our aliments, are all 

 alimentary principles without nitrogen. 



Of tho organic alimentary principles, the albuminous 

 substances, tho colouring matter of the blood, and the 

 gelatine, all contain nitrogen. 



The aliments which are composed of various alimentary 

 principles cannot be classified, in a similar way, on any 

 chemical basis into different groups; for the same ali- 

 uy principles appear in the most different aliments, 

 and their distinction depends either upon the quantitative 

 proportion of the corresponding constituents, or upon 

 some freshly supervening substances ; but there is so 

 great a variety, both in tho proportion in which the 

 ordinary alimentary substances are combined in the 

 aliments, and in the nature and qualities of tho super- 

 added substances, that the aliments classified with respect 

 to their chemical properties could be united into very 

 small groups only a circumstance which would render 

 difficult the review of tho whole. 



We have not, therefore, departed from the classification 

 which \ias hitherto been popularly employed, but shall 

 treat in succession on solid and liquid food, and or 



