ALIMENTARY CANAL. 35 



some of the Infusoria are as destitute of stomach and 

 mouth as vegetables. But before we speak particularly 

 of the digestive function, we will take a slight glance at 

 the various organs that are engaged in performing it. 



Emily. Pray, Dr. B., how many organs do you 

 reckon ? I had no idea of any other than the stomach, 

 and I cannot conceive why this is not sufficient. 



Dr. J3. It is because you take a partial view of the 

 function. Though the most important part of it is per- 

 formed in the stomach, yet there are several auxiliary 

 processes to be accomplished without which our food 

 would be but poorly digested. Before it is taker into 

 the stomach it must be torn in pieces and chewed by the 

 teeth and mixed with the fluids of the mouth. Then it 

 requires to be conveyed to the stomach which is ac- 

 complished by the act of swallowing, the result of a del- 

 icate contrivance in the mouth. After it has passed 

 through the stomach another cavity is prepared in which 

 it is mixed with the bile and other juices, and a system 

 of vessels to take it up and carry it into the blood. 



Emily. I was not aware till now of its being such a 

 complicated process, though 1 hope this will not induce 

 you to abbreviate your account from the fear of being 

 tedious ; I am sure J never shall lose my interest in your 

 instructions. 



Dr. B. It will not be necessary here, as well as in 

 other parts of the science to be very minute, for there 

 are many discussions and details wh'ich it would be use- 

 less for us to meddle with. We therefore, shall look 

 only to the most important and generally received views. 

 The digestive cavity, or alimentary canal as it is most 

 commonly called, is a long tube with a high degree of 

 vitality, provided with the necessary apparatus for secre- 

 ting the various fluids to be used in the digestive pro- 

 cess, varying in form, length and calibre according to 

 the habits of the species. This tube lies convoluted 

 upon itself, and is of very unequal capacity in its differ- 

 ent parts being capacious in the mouth, contracted in 

 the gullet, which again expands into the stomach, and 



