1896.J MICROSCOPICAL JOURNAL. 265 



are composed of cells, and studied some of them, animal or- 

 gans are likewise so made up. The cells of animal tissues 

 are so small and their walls are so delicate that it is not 

 possible to demonstrate them directly from fresh material 

 as in the case of plants, but the tissue must first be care- 

 fully preserved and then sections must be prepared from it. 

 Study the whole section with the low power and demon- 

 strate a general type of hepaticstrictliver tissueandbesides 

 certain other slices of ducts, vessels, etc.; which latter may 

 be ignored. Examine the liver cells and determine their 

 form and mutual relation. Do they come in contact 

 with their kind on all slides? Are they all of exactly 

 the same shape and size ? Can you recognize a distinct 

 wall, and is it thick, or thin ? How does the wall com- 

 pare with that of the onion cell or of cells in the potato? 

 Is the cell filled with granular stainable protoplasm ? 

 Is there a nucleus? Do you find a definite wall bound- 

 ing the nucleus.'' Has it a definite content? Does the 

 content appear to be of a protoplasmic nature ? Can you 

 recognize distinct parts nucleoli in the nucleus ? Find 

 a place in the section which adequately illustrates the 

 these points and make an exact drawing of it. 



(5. Summary of Part I. — Review all the studies thus 

 far made and test the following statements, using them as 

 evidence : The cell is a minute object, composed of pro- 

 toplasm, it has a definitely shaped nucleus, and is en- 

 closed by a wall which may be either thick, in plant cells, 

 or thin and flexible, in animal cells. Cells are massed 

 in great numbers and thus compose the tissues of living 

 objects, the grouping of which gives the object as it 

 is known to us through our ordinary senses. In scien- 

 tific language a part composed of tissues of an animal 

 or a plant is an " organ." The arrangement of the tis- 

 sues and organs of living things always obeys a certain 

 law peculiar to each being or group, called its "sym- 

 metry," beings may vary inside of narrow limits, and in 



