30 GEXKK.U. SKEJ'C// OF THE CELL 



between " protoplasmic " and " nieta]:)lasniic " substances, while a 

 real and necessary one, becomes after all one of degree. I believe 

 that we are probably justified in regarding the continuous substance 

 as the most constant and active element, and that which forms the 

 fundamental basis of the system, transforming itself into granules, 

 drops, fibrillac^, or networks in accordance with varying physiological 

 needs. ^ 



Thus stated, the question as to the relative activity of the various 

 elements becomes a real and important one. It now seems probable 

 that the substance of the meshwork (fibrillar or interalveolar structure) 

 is most active in the processes of cell-division, in contractile organs 

 such as cilia and muscle-fibres, and in nerve-cells ; but the ground- 

 substance, while apparently the most frequent seat of metaplasmic 

 deposits, is certainly also the seat of active chemical changes. This 

 subject has, however, not yet been sufficiently investigated. 



C. The Nucleus 



A fragment of a cell deprived of its nucleus may live for a consid- 

 erable time and manifest the power of coordinated movement without 

 perceptible impairment. Such a mass of protoplasm is, however, 

 devoid of the powers of assimilation, growth, and repair, and sooner 

 or later dies. In other words, those functions that involve destructive 

 metabolism may continue for a time in the absence of the nucleus ; 

 those that involve constructive metabolism cease with its removal. 

 There is, therefore, strong reason to believe that the nucleus plays an 

 essential part in the constructive metabolism of the cell, and through 

 this is especially concerned with the formative processes involved in 

 growth and development. For these and many other reasons, to be 

 discussed hereafter, the nucleus is generally regarded as a controlling 



1 Wilson, '99. Cf. Sachs ("92. '95), Kolliker ('97), Meyer ('96), and Kupffer ('96) on 

 energitls. Sachs sharply distinguishes between the encrgid (nucleus and protoplasm), which 

 forms a living unit, and the passive ^w^xgiA-prodncts, placing in the former the nucleus, 

 nucleolus, general cytojjlasni, centrosome and plastids (chloroplasts and leucoplasts), and in 

 the latter the starch-grains, aleurone-crystals, and membrane. Meyer carries the analysis 

 further, classifying the active energid-elements mio frotoplasnia/ic and alloplasmadc organs, 

 -tie former (nucleus cytoplasm, chromatophores, and perhaps the centrosomes) arising only 

 by division, the latter (cilia, and according to Kolliker, also the muscle- and nerve-hbrillse) 

 formed by differentiation from the protoplasmatic elements. The passive energid-products 

 {ergastic structures or " formed material " of Beale) are formed as enclosures (starch-grains, 

 etc.), or excretions (membranes). These general views are accepted by Kolliker; but 

 none of these writers has undertaken to show how " alloplasmatic " structures are to be 

 distinguished from metaplasmic or ergastic. I believe Sachs' view to be in principle not 

 only true but of high utility. Practically, however, it involves us in considerable difficultv, 

 unless the terminology adopted above — itself directly suggested by and nearly agreeing with 

 the usage of Sachs and Kolliker — be employed. 



