232 PROTOPLASM 



elastic properties must be present, as proteins are, without a 

 known exception, elastic. 



Attention is called by Scarth to the remarkable elastic and 

 rigid properties of protoplasm. He shows that strands of 

 streaming protoplasm may be so rigid that when slowly stretched 

 (by swelling in water) they suddenly snap across and then 

 crumple up on the recoil like a soUd thread and not like a fluid. 

 Yet almost immediately they show fluid properties again in that 

 the protoplasm begins to stream. 



The simplest and most convincing way to demonstrate the 

 elasticity of protoplasm is to stretch it between microneedles. 



Fiu. 111. — The stretching of protoplasm with the aid of a microneedle. 



One may or may not, in such an experiment, be handling living 

 protoplasm. Usually, however, one can tell fairly well in what 

 condition the protoplasm is. Death is ordinarily accompanied 

 by coagulation, and a coagulum is poorly extensile. Living 

 protoplasm may be stretched into very fine threads. The 

 epidermal cells of onion leaves are good material for such a 

 study. The cehs are plasmolyzed (the protoplasm shrunken 

 away from the cell wall), and the tissue cut across, thus open- 

 ing some of the cells without touching the protoplasm within 

 (page 61, Fig. 8). The cells may then be entered by a needle, 

 and the naked protoplasm touched. If the protoplasm is 

 sufficiently glutinous (sticky), as it usually is, it will adhere to 

 the needle and may then be drawn out to great lengths (Fig. 111). 

 When the protoplasmic thread snaps, its elastic limit has been 

 passed. A stretched protoplasmic thread may become so fine 

 as to be invisible under the highest power of the microscope. 

 Evidence of its persistence is given by the presence of globules 

 along its length, which continue to move apart from one another 

 and away from the cell as the needle is withdrawn. If stretching 

 is continued, the thread eventually breaks and then contracts, 

 moving so rapidly at first that it may double back on itself like 



