128 PHYSIOLOGY AT THE FARM. 



must be confessed, however, that the proportion of urea in 

 the urine seems to increase by an increase in the quantity 

 of nitrogenised aliment ; so that though an increase of mus- 

 cular exertion causes an increase of urea in the urine, yet that 

 the estimate of that increase will not exhibit the quantity of 

 organic tissue destroyed, unless the nitrogenised food remain 

 unchanged in the mean time. 



From these considerations it sufficiently appears that a 

 constant drain exists on the blood, standing, as it does, in- 

 termediate between the aliment on the one hand and the 

 organism and secretions on the other. 



Chyme. The blood, then, derives its repair, in some degree 

 it may be, from the stomach, but principally from the duo- 

 denum and the upper parts of the jejunum. The partially 

 changed mass descends from the fourth stomach, under the 

 name of chyme, into the duodenum. There the agents by 

 which further important changes are made on the alimentary 

 mass are the peculiar secretions of the intestinal mucous 

 membrane and glands of the duodenum, the secretion of the 

 liver or the bile, and the secretion of the pancreas or sweet- 

 bread. 



The chyme, as it passes from the fourth stomach into the 

 duodenum, is a greyish, semi-fluid, apparently homogeneous 

 substance, slightly acid in taste, otherwise insipid. Some kinds 

 of food give it a creamy aspect ; but when derived from fari- 

 naceous food, it has the aspect of gruel. The albuminoid parts 

 of the food, whether in the form of fibrine, albumen, or caseine, 

 principally exist in chyme in the state of albumen ; yet some 

 portions of these seem to remain in it still undissolved. Gummy 

 matters, unless in the forms incapable of solution, exist in the 

 chyme dissolved. The starch in the ox, as it would seem, is 

 almost entirely converted into sugar before it reaches the duo- 

 denum. Oily matters are reduced to very minute particles, 



