CHAPTER HI 



PROTOPLASM 



In his famous essay on protoplasm in 1868 Huxley very fittingly 

 referred to it as "the physical basis of life." With a realization of the 

 full significance of this phrase there comes the conviction that protoplasm 

 is the most interesting and important substance to which we can turn our 

 attention, for with it the phenomena of life, in so far as we know them, 

 are invariably associated. 



In spite of the enormous amount of work which has been done upon 

 protoplasm during many years, our knowledge of it must still be regarded 

 as very superficial and fragmentary. We can scarcely yet say definitely 

 that a given kind of protoplasm is not a single complex chemical com- 

 pound, as is held by one prominent school of biochemists: all ordinary 

 analysis seems to indicate that it represents a somewhat looser combina- 

 tion of substances, many of which are in turn very elaborate in composi- 

 tion; and further that these substances probably differ from those found 

 elsewhere not in any fundamental manner, but only in the degree of their 

 complexity. Proteins, fats, crystalloids, water, and other compounds 

 make up protoplasm, but protoplasm is not a mere mixture of these 

 materials; it is organized it is a system of complex substances, the 

 activities of which are fully coordinated. Only if we recognize in pro- 

 toplasm an organization can we conceive of it as a physico-chemical 

 substratum for those peculiar orderly activities characterizing living 

 substance, namely, synthetic metabolism, reproduction, irritability, and 

 adaptive response. 



Physical Properties. Certain early ideas regarding the physical 

 nature of protoplasm may be briefly reviewed at this point. 



Protoplasm appeared to its earliest observers merely as a colorless, 

 viscid substance containing minute granules. Two general opinions 

 soon developed: some held that protoplasm consists of but a single fluid, 

 whereas others regarded it as a combination of two fluids. Briicke 

 (1861), who was one of the first to lay emphasis on the fact that pro- 

 toplasm is an organized substance, looked upon the cell body as a con- 

 tractile, semi-solid material through which there streams a fluid carrying 

 granules. Similar to this was the idea of Cienkowski (1863), who be- 

 lieved he saw in the protoplasm of myxomycetes two fluids, one of them 

 hyaline and only semi-fluid (the "ground substance"), and the other 

 a more limpid fluid with granules suspended in it. De Bary (1859, 



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