CHAP, xxii.] DIET. 155 



needed, as a principal portion of the diet, to supply the waste which 

 mental and bodily exertion gives rise to. 



It must be confessed, however, that the views which theory sug- 

 gests upon this subject are not such as would enable us with benefit, 

 or even with safety, to determine the suitable diet for man. We 

 learn much from instinct and more from experience, which we could 

 never have gathered from a priori reasoning. Thus the importance 

 of the admixture of vegetable with animal food could never have 

 been determined without the aid of the experience afforded by the 

 melancholy instances of disease generated by the privation of the 

 former kind of aliment. Scurvy, as it is now well known, is fre- 

 quently due to the want of a proper supply of fresh vegetable food ; 

 and it may be quickly and effectually cured by supplying this want- 

 Again, it cannot be the deficiency of any of the staminal principles 

 which gives rise to scurvy, because these exist in abundance in the 

 animal food ; and scurvy, it must be remembered, will occur in the 

 midst of plenty of this kind of food. The disease is due to the 

 deficiency of some unknown material necessary to health, which 

 the vegetable kingdom alone can supply; and which, appa- 

 rently, is most readily obtained from citric acid, lemon or lime- 

 juice, or vegetables containing citric acid in good quantity, as the 

 potatoe. 



Nevertheless, the results of investigations as to the influence 

 of particular kinds of diet in modifying nutrition, are strongly 

 confirmatory of the views expressed above. Diet may be insuffi- 

 cient, either from its being given in too small quantity, or from its 

 being defective in some principle, essential or incidental, necessary 

 to the health of the blood that fluid, upon the healthy condition of 

 which the proper nourishment of the body depends. The effects 

 of a diet scanty in quantity, although not objectionable in quality, 

 are visible in the general emaciation, the wasting of all the tissues, 

 and the consequent debility. If dissolution be slow, the great non- 

 nitrogenized material of the body, fat, is employed to supply the 

 animal heat, as is strikingly seen in hybernating animals. Specific 

 effects follow the absence of certain elements of the food, even al- 

 though the absolute quantity of it be abundant. If nitrogen be 

 deficient in quantity, or altogether absent, the imperfect nutrition 

 shows itself in the form of ulcerations of particular textures. Those 

 tissues suffer most in which there is but little inherent activity of 

 nutrition, or which are exposed to the contact of vitiated secretions. 

 In Magendie's well-known experiments of feeding dogs upon sugar 

 and water, the cornea of the eye ulcerated, and destruction of the 



