

LABORATORY STUDIES AND DEMONSTRATIONS. 207 



surface (stained with dilute iodine to show nuclei and starch- 

 grains), and frog's or newt's blood, mixed with normal salt solu- 

 tion, and examined either fresh or slightly stained with dilute 

 iodine. 



Thin sections of pith (elder, etc.), from which the air ha& 

 been displaced by alcohol, give good pictures of tissue composed 

 of empty cells. Fresh or alcoholic muscle from the frog's leg, 

 gently teased out, shows muscular tissue to be composed of elon- 

 gated cells (fibres). Finally, the student may prove that he 

 himself is composed of cells by gently scraping the inside of his. 

 lip or cheek with a scalpel, mounting the scrapings on a slide, 

 and after adding a drop of Delafield's haematoxylin, covering, 

 and examining in the usual way. 



To show the lifeless matter in living tissue it suffices to ex- 

 amine frog's blood or human blood; sections of potatoes, es- 

 pecially if lightly stained with iodine ; sections of geranium stems. 

 (Pelargonium), which usually show crystals in some of the more 

 peripheral cells ; cartilage, stained with iodine, in which the life- 

 less matrix remains uncolored ; or prepared sections of bone, in 

 which the spaces once tilled by the living cells are now black and 

 opaque, being filled with dust in the grinding, or with air. 



CHAPTER III. (PROTOPLASM AND THE CELL.) 



Naked-eye Examination of Protoplasm. A drop of proto- 

 plasm is readily obtained from one of the long (internodal) cells. 

 of Nitella, after removing the superfluous water and snipping off 

 one end of the cell with scissors. The cell collapses and the 

 drop forms at the lower (cut) end. It may be transferred to a 

 (dry) slide and tested for its viscidity by touching it with a 

 needle. Microscopically it is instructive chiefly by its lack of 

 marked structure. 



The Parts of the Cell. The structure of the cell is beauti- 

 fully shown in properly stained and mounted preparations of un- 

 fertilized star-fish or sea-urchin eggs, or of apical buds of Nitella. 

 If these are not available potato-cells or cartilage cells do very 

 well ; or sections of epithelium, glands, etc. , may be shown. 



The class may also mount and draw frog's or newt's blood- 

 .cells, prepared and double-stained as follows. The blood is spread 



