STRUCTURAL BASIS OF PROTOPLASM 23 



is concerned in the process of cell-division and in the fertilization of 

 the Qgg, and has been characterized as the " dynamic centre " of the 

 cell. Whether it has such a significance, and whether it is in point 

 of morphological persistence comparable with the nucleus, are ques- 

 tions still sub judicc, which will be discussed elsewhere. ^ 



B. Structural Basis of Protoplasm 



As ordinarily seen under moderate powers of the microscope, proto- 

 plasm appears as a more or less vague granular substance which 

 shows as a rule no definite structure organization. More precise 

 examination under high powers, especially after treatment by suitable 

 fixing and staining reagents, often reveals a highly complex structure 

 in both nucleus and cytoplasm. Since the fundamental activities of 

 protoplasm are everywhere of the same nature, investigators have 

 naturally sought to discover a corresponding fundamental morpho- 

 logical organization common to all forms of protoplasm and under- 

 lying all of its special modifications. Up to the present time, however, 

 these attempts have not resulted in any consensus of opinion as to 

 whether such a common organization exists. In many forms of proto- 

 plasm, both in life and after fixation by reagents, the basis of the 

 structure is a more or less regular framework or mesJnvork, consisting 

 of at least two substances. One of these forms the substance of the 

 meshwork proper ; the other, often called the ground-substance (also 

 cell-sap, enchylema, hyaloplasma, paramitome, interfilar substance, 

 etc.), 2 occupies the intervening spaces. To these two elements must 

 be added minute, deeply staining granules or " microsomes " scattered 

 along the branches of the meshwork, sometimes quite irregularly, 

 sometimes with such regularity that the meshwork seems to be built 

 of them. Besides the foregoing three elements, which we may pro- 

 visionally regard as constituting the active substance, the protoplasm 

 almost invariably contains various passive or metaplasmic substances 

 in the form of larger granules, drops of liquid, crystalloid bodies, and 

 the like. These bodies, which usually lie in the spaces of the mesh- 

 work, are often difficult to distinguish from the microsomes lying in 

 the meshwork proper — indeed, it is by no means certain that any 

 adequate ground of distinction exists.^ 



From the time of Frommann and Arnold {'6s-'6y) onwards, most 

 of the earlier observers regarded the meshwork as a fibrillar structure, 

 either forming a continuous network or reticuluvi somewhat like the 

 fibrous network of a sponge (" reticular theory " of Klein , Van Bene- 

 den, Carnoy, Heitz mann), or consistmg of disconnected threads, 



1 Cf. pp. 304, 354. 2 cf. Glossary. ^ cf. p. 29. 



