THE COMPOSITION OF LIVING ORGANISMS. 21 



PRACTICAL STUDY. 



The student should understand, once for all, that the principal points 

 observed must be recorded by notes and by sketches, good or bad, whether 

 he can " draw" or not. Sketches should be first made in outline, should 

 be simple and on a large scale. They can afterwards be made very clear 

 by slightly shading the different parts with colored pencils. The aim should 

 be to represent the natural relations of parts rather than their minute 

 details, and accidental displacements should be disregarded. 



A. Organs. 



1. Examine and enumerate the more important organs of 

 some familiar dissected animal, e.g., a cat, frog, or pigeon. Make 

 a sketch showing the position of these organs, appending a list of 

 their functions so far as von can determine them from your 

 general knowledge. 



2. Make a like examination of some familiar flowering plant ; 

 e.g., a lily or geranium. "What general resemblances, and what 

 differences, between plant and animal do you find ? 



B. Tissues. 



1. Prepare (or examine) the leg, or some other organ, of a 

 mammal or frog so dissected as to show some of the component 

 tissues. Learn their names from the demonstrator and make 

 a sketch showing the appearance and relative position of at least 

 three of them. 



2. Study the leaf of a plant. Observe the following tissues ; 



a. Skin or epidermis, which, after moistening, may easily 



be scraped off with, a knife. 



b. Supporting tissue the network of veins or nerves. 



c. Mesophyll the green pulp. 



C. Cells. 



1. Make with a sharp razor a thin slice or " section" of the 

 stalk of a large leaf (or of a succulent young stem, e.g., of celery). 

 Mount in water and study it with the microscope, at first with a 

 low power, afterwards with a higher. Sketch some of the cells. 



2. "With a pair of forceps tear off a bit of epidermis from the 

 upper surface of a leaf ; mount in water, examine it with the 

 microscope and sketch a few cells. 



3. Examine with the microscope a drop of newt's or frog's 

 blood. Sketch some of the cells (corpuscles). 



