84 PHYSIOLOGY FOR THE LABORATORY. 



now thought that the epithelial membrane, composed of a 

 single layer of cells, takes an active part in the absorption 

 of the soluble, products of digestion.- The laws that 

 control living cells are probably different from those of 

 4 imbibition ' and t osmosis ' with a dead membrane. But 

 as these physical laws may aid in absorption they should 

 not be disregarded. 



I. THE EPITHELIAL CELLS. 



Review the microscopical slide showing a section of 

 the wall of the small intestine. Recall particularly the 

 epithelial cells, their shape, size, arrangement, and the 

 number of layers. 



II. DIFFUSION. 



Materials. 20 c.c. of water. lOc.c. of oil. 5 c.c. of ink. 

 Apparatus. Test-tubes. 



Experiment : 



1. Shake 10 c.c. of water and 10 c.c. of oil together. 



Do they mix or diffuse ? 



2. Shake the water and ink. Do they mix ? What 



is meant by diffusion ? Why do the water and 

 ink diffuse while the water and oil do not? 



III. OSMOSIS. 



Materials. Two eggs. A cup of vinegar. Dextrose. 

 Apparatus. A large beaker. Tape-measure. 



Experiment : 



1. Measure the circumference of an egg around 

 the short axis and around the long axis, and 

 make a record of the measurements. 



