PROTOPLASM OF PROTOZOA 95 



Many other observers, using microdissection methods, have confirmed 

 this for a whole series of animal and plant cells. The spinning of threads 

 from protoplasm is generally assumed to be dependent upon the sub- 

 microscopic fibrillar structure of the protoplasm, the latter being respon- 

 sible for its elasticity and high degree of extensibility. The tensile strength 

 of a strand of myxomycete protoplasm has been found by Pfeffer (quoted 

 by Seifriz, 1936) to be 50 mgm. per square millimeter. The ropiness of 

 protoplasm is of course conditioned by temperature, viscosity, hydrogen- 

 ion concentration, and other factors which affect protoplasm (review 

 byjochims, 1930). 



Further evidence of the micellar nature of protoplasm may be deduced 

 from the experiments of Seifriz (1936), who has examined the proto- 

 plasm of slime molds with a Spierer lens. When the protoplasm is quiet 

 it presents a mosaic appearance, but when in active flow or when formed 

 into a thread is presents a striated appearance. Harvey and Marsland 

 (1932) noted that the crystals of Amoeba fall in jerks when moving 

 under centrifugal force; this may be due to the presence of structural 

 elements in the protoplasm. Moore (1935) has found that slime molds 

 in the plasmodial stage will flow through pores 1 p in diameter. He also 

 forced this living material through bolting cloth of various mesh sizes. 

 The Plasmodia survived after being forced through pores 0.20 mm. in 

 diameter or larger, but died when forced through smaller pores. Moore 

 thinks that there are fibrillar elements in slime mold protoplasm which 

 are destroyed if forced unoriented through a pore through which they 

 could flow if the micelles were properly oriented. 



DOUBLE REFRACTION 



The great advantage of the use of the polarizing microscope is that 

 characteristic structure which is otherwise imperceptible may be revealed, 

 even in the living organism, without any alteration of the specimen. 

 Amorphous and pseudoamorphous materials (i.e., materials in which 

 the orientation of the particles is a random one) are dark when viewed 

 between crossed nicol prisms. True double refraction is always the re- 

 sult of an orientation of optically anisotropic elements; many substances, 

 such as glass, become doubly refractive if deformed by external forces. 

 Many sols when in movement or when placed in an electric or a magnetic 



