STRUCTURAL BASIS OF PROTOPLASM 



29 



cells, or of certain physiological conditions,^ none is common to all 

 forms of protoplasm. If this position be well grounded, we must 

 admit that the attempt to find in visible protoplasmic structure any 

 adequate insight into its fundamental modes of physiological activity 

 has thus far proved fruitless. We must rather seek the source of 

 these activities in the ultramicroscopical organization, accepting the 

 probability that apparently homogeneous protoplasm is a complex 

 mixture of substances which may assume various forms of visible 

 structure according to its modes of activity. 



Some of the theoretical speculations regarding the essential nature 

 of that organization are discussed in Chapter VI., but one q2iasi-X\\(to- ' 

 retical point must be here considered. Much discussion has been 

 given to the (question as to which of the visible elements of the proto- 

 plasm should be regarded as the "living" substance proper; and the 

 diversity of opinion on this subject may be judged by the fact that 

 although many of the earlier observers identified the "reticulum " as 

 the living element, and the ground-substance as Ufeless, others, such 

 as Leydig and Schafer, held exactly the reverse view, while Altmann 

 insisted that only the " granules " were alive. Later discussions have 

 shown the futility of this discussion, which is indeed largely a verbal 

 one, turning as it does on the sense of the word "living." In practice 

 we continually use the word "living" to denote various degrees of 

 vital activity. Protoplasm deprived of nuclear matter has lost, wholly 

 or in part, one of the most characteristic vital properties, namely, the 

 power of synthetic metaboHsm ; yet we still speak of it as " living," 

 since it still retains for a longer or shorter period such properties 

 as irritability and the power of coordinated movement ; and, in like 

 manner, various special elements of protoplasm may be termed " liv- 

 ing " in a still more restricted sense. In its fullest meaning, however, 

 the word "living" implies the existence of a group of cooperating 

 activities more complex than those manifested by any one substance 

 or structural element. I am therefore entirely in accord with the 

 view urged by Sachs, Kolliker, Verworn, and other recent writers, 

 that life can 'only be properly regarded as a property of the cell- 

 system as a whole ; and the separate elements of the system would, 

 with Sachs, better be designated as "active" or "passive," rather 

 than as "living" or "lifeless." Thus regarded, the distinction 



1 Thus the alveolar structure seems to be characteristic of Protozoa in general, and of 

 the protoplasm of plant-cells when in the vegetative state, the fibrillar of nerve-cells and 

 muscle-cells. The granular type is characteristic of some forms of leucocytes and gland- 

 cells; but many of the granules in these cells are no doubt metaplasmic, and it is further 

 very doubtful whether such a granular or "pseudo-alveolar" structure can be logically dis- 

 tinguished from an alveolar (c/. Wilson, '99). In the pancreas-cell granular and hbr.llar 

 structures alternate with the varying phases of secretory activity {r/. Mathews, '99). 



