248 OF FOOD AND THE DIGESTIVE PROCESS. 



432. Various circumstances lead to the belief, that the saccharine 

 compounds are thus carried off by the respiratory process, within a short 

 time after they have been introduced into the system. They have not 

 been detected in the chyle drawn from the lacteal absorbents ; but there 

 seems reason to believe that, in consequence of their ready solubility, 

 they are directly taken up by the blood ( 493), and that they are so 

 rapidly burned off there, as to escape notice in that fluid. But it has 

 been lately shown by Dr. Buchanan, that, if the blood be examined 

 within a short time after a meal consisting in part of farinaceous and 

 saccharine substances, a very appreciable quantity of saccharine matter 

 is found in it. This soon disappears, however, being eliminated or sepa- 

 rated from the blood by the action of the lungs. In fact it is very pro- 

 bable, that a large proportion of the matter thus taken in never enters 

 the general circulation at all ; as the blood of the mesenteric veins pro- 

 ceeds to the lungs, after passing through the liver, before it is trans- 

 mitted to the systemic arteries, and may there lose its saccharine matter, 

 as fast as this is taken in from the stomach. After a meal containing the 

 ordinary admixture of saccharine, oily, and albuminous compounds, it is 

 probable that the saccharine are first received into the blood, and are 

 the first to be eliminated from it ; and that, by the time they have been 

 all consumed, the oily matter, introduced through the more circuitous 

 channel of the lacteal system, is ready to answer the same purpose. If 

 these are exhausted before a fresh supply of food is taken in, cold as 

 well as hunger is experienced ; and the body is in this condition pecu- 

 liarly liable to suffer from any depressing causes, such as a low external 

 temperature, poisonous miasmata, &c. ; hence the prudence of avoiding 

 exposure to such influences upon an empty stomach. 



433. We can thus in part account for the fact, which universal expe- 

 rience has established, that in warm-blooded animals, a mixture of azo- 

 tized and non-azotized substances is the diet most conducive to the welfare 

 of the body ; and that, in all but the purely carnivorous tribes, the diet 

 provided by Nature consists not only of albuminous, gelatinous, and oily 

 substances, such as are furnished by the flesh and fat of animals, but 

 also of saccharine or farinaceous matter. This is the diet to which Man 

 is evidently best adapted ; and it is remarkable how completely accordant 

 is his use of the ordinary materials of food, with the principles now es- 

 tablished by chemical and physiological research, in regard to the wants 

 of his bodily system, and the best mode of supplying them. Thus, good 

 wheaten bread contains, more nearly than any other substance in ordi- 

 nary use, that proportion of azotized and non-azotized matter, which 

 is adapted to repair the waste of the system, and to supply the neces- 

 sary amount of combustible material, under the ordinary conditions of 

 civilized life in temperate climates ; and we find that the health and 

 strength can be more perfectly sustained upon that substance, than upon 

 any other^taken alone. The addition of a moderate quantity of butter 

 increases its heat-producing powers : and this is especially useful when 

 the temperature is low, under which condition there is usually an in- 

 creased disposition to the employment of fatty matters as articles of 

 food. On ^the other hand, if the body be subject to violent exertion, 

 advantage is gained by increasing the proportion of the proteine-com- 

 pounds, by the addition of animal flesh ; and, under any circumstances, 



