THE PROTOPLASMIC SYSTEM 



when isolated from, and free of, cytoplasmic inclusions is 

 wholly viable. I refer to that branch of chemistry, colloid 

 chemistry, so-called, where fact and fancy are dispersed in 

 the medium of a naivete which so often characterizes new 

 adventures along narrow confines. 



An e^^ like that of Nereis in which the formed bodies, 

 oil-drops and yolk spheres, are visible when magnified only 

 twenty times can not with respect to these bodies be con- 

 sidered by a colloid chemist as other than an extremely 

 coarse suspension. It can not be regarded as a colloidal 

 solution for a colloidal solution is usually defined as one in 

 which the particles range in size from i, 2 or 6 to 250 {xix. 

 The smallest are at the lowest limits of visibility with the 

 ultra-microscope and the largest come just within range of 

 microscopic observation. Even such eggs as sea-urchins', 

 whose oil-drops, yolk-spheres and pigment granules are 

 smaller than the oil-drops and yolk-spheres of the Nereis 

 Qgg, can not be looked upon as colloidal solution for their 

 inclusions are visible under relatively low power of the 

 microscope and thus do not fall within the range of sizes of 

 particles in a colloidal solution. But the ground-substance 

 of these eggs is a colloidal solution since its particles, barely 

 visible under the highest powers of the microscope, are 

 more clearly revealed by dark-field illumination. 



The definition of cytoplasm here given also means dis- 

 carding theories of the morphological structure of cytoplasm 

 since these, the alveolar, filar and granular theories, refer 

 to the cytoplasm plus inclusions. 



Even if we would define cytoplasm to embrace the cyto- 

 plasmic inclusions, the alveolar theory of cytoplasmic 

 structure would be untenable. In the first place, although 

 it is true that there are cells which show a vacuolated or 

 foam structure, this is by no means all-pervading but is 

 limited to certain cellular regions. Moreover, such struc- 

 ture is far from being demonstrable in all cells and the 



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