MICRURGY 



61 



The Amoeba nucleus can be liberated by pinching off a bit of 

 the animal with the nucleus. When thus freed and penetrated 

 by two microneedles, the (now coagulated) nucleus is found to 

 possess a very delicate membrane which can be lifted off like a 

 thin veil (Fig. 48). 



Fig. 48. — The isolated, degenerate Amoeba nucleus from which the coagulated 

 nuclear membrane has been partially separated by stretching. 



Plant tissue, in spite of its rigid wall, serves as interesting 

 material for a variety of studies. Very satisfactory is the 

 epidermis of onion scale leaves, when properly handled. These 

 cells are alive, even though the onion has rested for weeks in 

 storage. If a bit of the epidermis 

 is peeled off and placed in a sugar 

 or salt solution of suitable con- 

 centration, the living protoplasm 

 in each cell shrinks up into a ball 

 within the cellulose box that con- 

 stitutes the cell casing. This is fi^. 49.— The exposed living 



the phenomenon of plasmolysis protoplast of a cell indented by 



(page 194). If a strip of this tissue 



is cut across with a sharp knife, some of the cells, i.e., the rigid 

 cellulose boxes, will be cut close to their ends, leaving the living 

 protoplasm exposed and untouched within (Fig. 8). The epi- 

 dermis is then mounted in a hanging drop of water on the under- 

 side of the cover of the moist chamber (Fig. 40). A specially 

 constructed needle is used ; it is manipulated so as to enter the cell 

 through the open end and to come into contact with the naked 

 protoplasm (Fig. 47i)). The ball of protoplasm can be indented 

 (Fig. 49), and an idea of the turgidity of its vacuole gained. 



