284 A MANUAL OF VETERINARY PHYSIOLOGY 



must not, however, be supposed that absorption in the latter is 

 exclusively carried on by the bloodvessels, for remembering the 

 large chain of glands, along the colon in particular, it is probable 

 that the material absorbed passes through these glands to a 

 greater or less extent, as in the mesentery, before entering the 

 circulation. There is, at any rate, a well-developed lymphatic 

 system in the walls of the large intestine, and it is certain that 

 material is taken up from this bowel both by the bloodvessels 

 and lymphatics. The amount of this must be considerable, 

 when the size of these bowels is borne in mind and the character 

 of their contents. 



Substances can be taken up with extreme rapidity from the 

 large bowels. Colin observed that eighteen minutes after in- 

 jecting a solution of nux vomica into the caecum of the horse 

 convulsions began, and eight minutes later the animal was dead. 

 Anaesthetics, such as ether, may also be administered per rectum 

 and produce narcosis. Finally, and from some points of view 

 most important of all, proteids may be absorbed from the rectum 

 and single colon, in spite of the fact that there is no proteolytic 

 ferment to render them soluble. 



Absorption of Fat. — If a cannula be placed in the thoracic duct 

 of a starving dog, the lymph which escapes is identical with that 

 from any other part of the body. If the animal be now fed on 

 a diet rich in fat, the lymph becomes milky, and even the blood 

 plasma becomes turbid from fat, if the contents of the duct are 

 permitted to enter the general circulation. It is evident that 

 the lymphatics are the chief path by which the fat enters the 

 body, for comparative analysis of the blood of the portal vein 

 and carotid artery shows that the amount of fat in the two is 

 the same. Nevertheless, the bloodvessels are not without some 

 action in the matter, the evidence being that from an open 

 thoracic duct not more than 60 per cent, of the total fat given 

 in an experimental diet can be recovered ; after deducting that 

 excreted unabsorbed with the faeces, there still remains a balance 

 unaccounted for. The missing portion of fat is believed to be 

 absorbed by the bloodvessels. 



It has been shown (p. 256) that fat in the small intestine is 

 both saponified and emulsified, the former being a chemical, 

 the latter a physical change. These processes result from the 

 separate and combined action of the pancreatic juice and bile, 

 and they lead to two possible views as to the mechanism of fat 

 absorption. Emulsification reduces the fat (and fatty acids) to 

 a state of subdivision into particles so minute that they might 

 conceivably be simply passed as such, through the epithelial cells 

 of the villi to the lacteals, by an activity of these cells comparable 

 to the ingestive powers of a white blood-corpuscle. This would 



