ci-.xr.RAi sk'i-.'rcn OF '/'///; CELL 



too, in his celebrated hypothesis of pangenesis, adopted a nearly 

 related conception, which as remodelled by De Vries twenty years 

 afterwards ('89) forms the basis of the theories of development 

 maintained by such leaders of biological research as Weismann and 

 Hertwig. The same view appears in a different form in the writ- 

 ings of Nageli, Wiesner, Foster, Verworn, and many other morpholo- 

 gists and physiologists. 1 



An hypothesis backed by such authority and based on evidence 

 drawn from sources so diverse cannot be lightly rejected. We are 

 compelled by the most stringent evidence to admit that the ultimate 

 basis of living matter is not a single chemical substance, but a mixture 

 of many substances tJiat arc self-perpetuating without loss of their 

 specific character. The open question is whether these substances 

 are localized in discrete morphological bodies aggregated to form the 

 cell somewhat as cells are aggregated to form tissues and organs, 

 and whether such bodies, if they exist, lie within the reach of the 

 microscope. Altmann's identification of the "granulum" as such a 

 body is undoubtedly premature ; it is certain that his description of 

 cell-structures from this point of view is often very inaccurate ; it 

 is extremely doubtful how far the granules or microsomes are normal 

 structures, and how far they are artefacts produced by the coagulat- 

 ing effect of the reagents. It is nevertheless certain, as will be 

 shown in Chapter VI., that at least one part of the cell, namely the 

 nucleus, actually consists of self-propagating units of a lower order 

 than itself, and there is some ground for regarding the cyto-micro- 

 somes in the same light. 



C. THE NUCLEUS 



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

 siderable time and manifest the power of co-ordinated movement 

 without perceptible impairment. Such a mass of protoplasm is, how- 

 ever, 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 



1 The following list includes only some of the various names that have been given to 

 these hypothetical units by modern writers: Physiological unit* (Spencer) ; gem mules 

 (Darwin); pangens (De Vries); plnsomes (Wiesnrr) ; micella (X;igeli); placidities 

 (Haeckel and Elssberg) ; inotagmata (Engelmann); biophores (Weismann); bioblasts 

 (Beale); somacules (Foster); idioblasts (Hertwig); idiosomes (Whitman); biogens (Ver- 

 worn); microzymas (Bechamp and Kstor) ; geinniie (Haacke). 



