62 PROTOPLASM 



The protoplast can be pulled out of the cell and dissected, when 

 properties of the isolated nucleus and vacuole can be determined, 

 such as the elasticity of the nucleoplasm, the nature of its 

 membrane, tolerance to dissection, and the effect of reagents. 

 Or we can direct our attention to the cellulose wall. The needle, 

 if sharp and rigid, can be forced through several cells, penetrating 

 the walls with ease (Fig. 8). Thus are some of the mechanical 

 properties of cell walls in the natural state revealed. 



The consistency of protoplasm has received much attention 

 from investigators. One method of ascertaining it is to observe 

 the behavior of protoplasm when needles are moved about in it. 

 The method does not permit of great accuracy but has several 

 advantages, such as permitting the various regions of a cell to 

 be explored. A novel method of determining protoplasmic 

 consistency, and its elastic qualities as well, is to insert in it a 

 metal particle which is then attracted by an electromagnet 

 (Fig. 35). The rate of movement of the particle gives an 

 indication of the viscosity of the protoplasm, and the distance 

 the particle returns when the magnetic force is removed is a 

 measure of the elasticity. A more satisfactory method of 

 ascertaining elastic values is to stretch protoplasm between 

 microneedles. The living substance is ordinarily highly elastic. 

 Convenient material for proving this is the protoplasm of slime 

 molds or the exposed protoplasts of the epidermal cells of the 

 onion just described. A needle is brought into contact with the 

 protoplasm; the latter, being sticky, adheres to the needle and 

 can then be stretched to great lengths (Fig. 111). The effect 

 of salts on the extensibility of protoplasm can be ascertained by 

 such experiments. It is found that the monovalent cations 

 sodium, potassium, and lithium, decrease the stretching limit of 

 protoplasm and that the bivalent metals cadmium and strontium 

 increase it, while magnesium has no effect. 



Microdissection studies may be carried out on the human 

 corpuscle. The dissection of the human erythrocyte represents 

 the ultimate in micrurgical technique. The blood cells measure 

 but 8 fx (0.008 mm.); the needle must, therefore, be the finest 

 that it is possible to make and be manipulated with perfect 

 control. It has been possible to tear open the human red 

 corpuscle and to establish the presence of a delicate membrane, 

 as in the case of the much larger amphibian corpuscle. 



