308 
A. H. LOGAN. 
ORIGINAL ARTICLES. 
THE CHANGES FOOD UNDERGOES IN ITS PASSAGE THROUGH 
THE DIGESTIVE TRACT, 
By A. H. Logan, V.S., Bellefontaine, Ohio. 
(A Paper read before the Ohio and Michigan Veterinary Societies.) 
The notice received by me to prepare a paper for discus¬ 
sion on this important occasion, was at such a late hour that 
I wrote our Secretary declining the honor. But on recon¬ 
sideration I withdrew my former objection and prepared a 
paper on “ The changes the food undergoes in its passage 
through the digestive tract.” 
It is not my intention to give a description of the organs 
comprising the digestive tract, and accessories thereto, as I 
presume you are all as thoroughly conversant with the 
anatomy of the parts as I am, but simply to state the vari¬ 
ous secretions desired to promote digestion, from whence ob¬ 
tained and their various actions upon the food. 
The food on entering the mouth undergoes two processes, 
viz. : Mastication and insalivation. The former is performed 
by the teeth, and the latter by a secretion called saliva, 
whieh is obtained from the salivary glands. 
The presence of food in the mouth excites the terminal 
fibres of the gustatory and glosso-pharyngeal nerves, which 
transmits the sensation to the medulla, the reflex action is re¬ 
turned along the chorda tympani and auriculo temporal 
nerves which, by inhibiting the sympathetic, dilates the blood 
vessels, and increases the functional activity of the salivary 
glands. Some say the chorda tympani contain fibres which 
directly stimulate the secreting epithelial cells. Stimulation 
of the vaso-motor nerves diminishes the supply of blood, by 
narrowing the caliber of the vessels, thereby lessening the 
secretion. The theory that saliva is produced by pressure 
alone is incorrect, as the pressure of saliva in the ducts is 
about twice as great as the blood in the blood vessels. Such 
being the case, and if due to pressure alone, the saliva would 
re-enter the blood vessels and lymphatics. 
