WHAT IS A GLAND? 361 



an insoluble to a soluble form, you remember, was brought about 

 by agents called enzymes. Several different kinds of enzymes were 

 found in the plant cells, and in those cells digestion took place. 



Somewhat the same condition exists in animals. If food is to 

 be of use to man, it must be changed into a soluble form that 

 can pass through the walls of the alimentary canal, or food tube. 

 This process is carried out by the various enzymes which bring 

 about digestion. 



In nearly all vertebrate animals, food is taken into the mouth and 

 passed through a food tube, in which it is digested. This tube is 

 composed of different portions, named, respectively, as we pass 

 from the mouth downward, pharynx (far 'inks), gullet, stomach, 

 small intestine, and large intestine. Attached to this food tube 

 or lying in its walls are structures called glands. It is within the 

 cells of these glands that the enzymes are manufactured which 

 cause digestion to take place. 



PROBLEM I. WHAT IS A GLAND AND HOW DOES IT DO 



ITS WORK? 



In addition to the alimentary canal proper, and connected with 

 it, we find a number of digestive glands. These are the salivary 

 glands of the mouth, the gastric glands of the stomach, the pan- 

 creas (pan'kre-as) and the liver, both connected with the small 

 intestine by ducts, and the intestinal glands in the walls of the 

 small intestine. Besides these glands which aid directly in diges- 

 tion, there are several others known as the endocrine (en'd6-krln) 

 or ductless glands, because they have no ducts or tubes to carry off 

 their contents. These glands give their secretions, which contain 

 substances known as hormones, directly into the blood. We shall 

 study their functions later. 



Demonstration It A simple gland. (Microscopic preparation.) 

 Under the microscope, notice the structure of a gland in both cross 

 and longitudinal sections. With what is the wall lined? What is 

 the shape of the gland ? If work is done by a gland, then it must have 

 fo,od to do this work. Might the material poured out of a gland be 

 manufactured from the food it gets ? 



What structures would of necessixy go to a gland to take food there? 

 Write a paragraph telling the uses and structure of a gland. 



