206 APPENDIX. 



reversal of the image in the latter), and should during the course 

 learn the nse of the camera kicida (Abbe's camera, of Zeiss, tlie 

 best). The stage-micrometer may also be examined at this time 

 or later, and the student taught to prepare a scale (see Andrews) 

 by drawing the lines, with camera, on a card under different 

 p>owers (A + 2, D + 2, D + 4, of Zeiss), and labelhng each 

 with the names of lenses and actual size of the spaces, as stated 

 on the micrometer. 



Pencil- drawing should begin as soon as the first sj^ecimen is 

 in focus, and sketches should be made, from the very first exercise 

 onward, of everything really studied. It is absolutely indis- 

 pensable to heej) a laboratory note-hooh^ which ought at any time 

 to give tangible evidence that the laboratory study is bearing 

 fruit ; and in the very first laboratory exercise a beginning should 

 be made in this direction. 



The preliminary microscopy of one or two laboratory peri- 

 ods, corresponding to the time spent in conferences U2)on the first 

 chapter of the text-book, leads naturally up to the easy micro- 

 scopical studies required in connection with the second chapter. 



ChAPTEK II. (STilUCTURE OF LiVING ORGANISMS.) 



The laboratory work may be made very brief and simple, 

 and the facts shown largely by illustration. Tlie principal 

 organs of a j)lant and of a five or dissected animal may be shown 

 and some of the more ob^dous tissues pointed out. A frog under 

 a bell-glass, and a flowering plant (geranium) in blossom, j)laced 

 side by side on the demonstration-table will serve to suggest 

 materials for the lists of organs and the comparisons called for. 



The skin of a Calla leaf is easily stripjDed off and demon- 

 strated to the naked eye as one form of tissue. It may then be 

 cut up and distributed for microscopic study and for j^roof that 

 it is composed of cells. (During this process air is apt to replace 

 water lost by evaporation, and must be displaced by alcohol, 

 which in turn must be removed by w^ater.) 



For a first microscopical examination of tissue there is no 

 better object than the leaf of a moss (a species having thin broad 

 leaves should be chosen) or a fern prothalHum. Otlier good 

 objects are thm sections of a potato-tuber from just helow the 



