NATURE AND DESTINATION OF FOOD. 101 



portions in the animal tissues, are principally derived from the vegetable 

 kingdom, in which they are frequently present to a large amount. The 

 pure sugars undergo little change before absorption, though they are some- 

 times partially decomposed into lactic and butyric acids. It *is probable 

 that cane-sugar undergoes conversion into grape-sugar either at the liver or 

 soon after it has entered the blood. Starch is for the most part converted 

 into dextrin and grape-sugar; and by a further process of oxidation or 

 combustion, these compounds generate carbonic acid, which is chiefly elimi- 

 nated by the lungs, and thus become directly subservient to the generation 

 of nervo-muscular force, and to the maintenance of the heat of the body. 

 That the saccharine substances are per se insufficient for the maintenance of 

 life has been shown by numerous experiments upon animals, and by the in- 

 teresting experiments of Dr. Hammond, 1 who on one occasion limited him- 

 self to a diet of !$ Ib. of gum per diem, and on another to a similar quantity 

 of starch and water. In both sets of experiments hunger, debility, and 

 febrile excitement were soon experienced, and he was finally compelled to 

 discontinue the gum diet on the fourth day, though he was able to persevere 

 in the use of the starch till the tenth a circumstance which was probably 

 partly due to its still retaining a small proportion of gluten, and partly to 

 its not producing such serious disorder of the stomach and bowels as the 

 gum. 



60. The Oleaginous compounds ( 56) which enter so largely into the 

 composition of the body being not only stored up in masses in the adipose 

 substance, but also forming constant and important constituents of the mus- 

 cular, nervous, and other tissues are partly introduced into the system 

 from without, and are also partly the result of the chemical metamorphoses 

 effected within the body upon the albuminous and saccharine compounds: 

 by which means the latter become subservient to the nutrition of the several 

 nitrogenous as well as non-nitrogenous tissues. In the diet of the Caruivora, 

 the fats almost entirely replace the carbohydrates consumed by the Her- 

 bivora. Previous to absorption the oleaginous substances undergo fine 

 division, and, perhaps, to some extent sapouitication ; whilst after their en- 

 trance into the circulation they are partly applied to the purposes of nutri- 

 tion, partly to the production of uervo-muscular force, and partly, there is 

 good reason for believing, combine immediately with oxygen, and thus sup- 

 port the animal heat. Like the saccharine, the oleaginous compounds when 

 consumed alone are wholly incapable of supporting life ; and the only 

 benefit that a starving animal obtains from their consumption is the main- 

 tenance of its temperature, and a consequent slight prolongation of its life ; 

 death occurring, as has been shown by Mr. Savory, when non-nitrogenous 

 food is freely supplied, 2 not from loss of temperature, as in inanition, but 

 from loss of tissue. The experiments of Dr. Ed. Smith on the elimination 

 of carbonic acid, and of MM. Fick and Wislicenus, and Dr. Parkes, on the 

 excretion of nitrogen during rest and exercise, as well as the more theo- 

 retical considerations adduced by Professor Frankland, alike tend to show 

 that during the period of active exertion the nitrogen-holding substance of 

 the muscles undergoes comparatively trifling increase in the disintegration 

 to which it is constantly subject, whilst a marked increase occurs in the 



to the right Changes essentially similar to those just described as produced in starch 

 by boiling with acid, are effected by the action of a ferment termed diastase, which 

 is developed in germinating seeds. Diastase breaks up starch into glycose and achroo- 

 dextrin, and if fermentation continues the latter is gradually almost wholly con- 

 verted into glycose. See Briicke, Vorlesungen, 1874. 



1 Experimental Researches on Food, Philadelphia, 1857. 



2 Proceedings of Royal Society, May 1st, 1862. 



