CHAPTER TV 

 PROTOPLASM 



Few scientific achievements rank in importance with the discovery 

 that the phenomena of hfe occur in a colorless, somewhat viscous fluid- 

 like material having certain properties common to all organisms. Every 

 plant and animal type, and probably every individual, has its own charac- 

 teristic type of protoplasm, but the fundamental features of this sub- 

 stance are strikingly the same everywhere. This highly significant fact 

 was given eloquent expression by Thomas Huxley (1868) in his classic 

 essay on "The Physical Basis of Life," which ranks as a masterpiece of 

 popular scientific exposition. 



Physical Characters of Protoplasm. — By direct observation with the 

 aid of the ordinary microscope, protoplasm is revealed as a clear fluid, 

 called hyaloplasm, in which there usually are distributed globules, 

 granules, and various special differentiations. Many activities, such as 

 the characteristic streaming in vacuolate plant cells and the responses to 

 certain experimental treatments, may be studied in this way, but the 

 investigator must employ additional special techniques. Among these 

 aids are dark-field illumination, which reveals the presence of very 

 minute particles; ultraviolet photography, which yields images showing 

 fine structural detail; fluorescence in ultraviolet light, which gives evi- 

 dence of composition; polarized light, by which it is possible to learn much 

 concerning ultramicroscopic structure and chemical composition; the 

 high-speed centrifuge, which yields data on specific gravity and viscosity; 

 the micromanipulator, wnth which it is possible to operate on living cells 

 under high magnifications; and the electron microscope. 



The results of such investigations have been numerous and of excep- 

 tional value. For example, it has been possible to measure with con- 

 siderable accuracy the viscosity of protoplasm in different cells, in 

 localized regions of the same cell, and in the same region at different 

 stages of functional activity. The values obtained range from only two 

 or three times that of water in the granule-free hyaloplasm of certain 

 eggs to hundreds of times this value in some other types of protoplasm. 

 Commonly the viscosity of protoplasm in active cells is about that of 

 glycerin or light machine oil. Exceedingly high values sometimes 

 reported are probably due to secondary differentiations in the protoplast. 

 The average viscosity tends to be lower in plants than in animals. 



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