BY W. J. BYRAM. XIU 



body. The result is very striking. The pieces which include 

 no portion of the nucleus continue to exhibit vital activities for 

 a time, but these soon come to an end, and death is the result. 

 On the other hand, the pieces which have retained portions of 

 the nucleus actually continue to carry on the vital activities and 

 to assimilate food and grow, as if no such partition had been 

 made. Here then, at once, we have a new restatement of the 

 cell theory. It is not the cell wall which is the essential 

 element, as Schleiden and Schwann thought, the protoplasmic 

 contents are not the all-in-all, as the observers which followed 

 them stated ; but, as far, at any rate, as the powers of food 

 assimilation, growth, and reproduction are concerned, the 

 nucleus is an all -important factor. But this discovery was 

 attended by another. The improvement in microscopes and 

 microscopical methods enabled observers to see that proto- 

 plasm is not by any means homogeneous or structureless, 

 and the former idea, that it is a chemical compound or 

 mixture of such, having life as its attribute, is aban- 

 doned, for protoplasm is found to consist of an infinitely 

 delicate network of slender fibres, forming a reticulated 

 material, which is interspersed with very minute granules known 

 as microsomes, and this network is filled with a transparent 

 fluid. It is therefore apparent that, as in the term " cell," the 

 essential idea to which the name " protoplasm " was given, has 

 actually vanished, and the name is only retained to designate 

 this conjunction of a filamentous network, and clear liquid, 

 which constitute part of the constituents of the biological unit. 

 Another complete change of conception has resulted from recent 

 research, for the nucleus itself instead of being, as was formerly 

 thought, a minute speck of protoplasm rather more dense than 

 that which surrounds it, is found to be a distinct element, itself 

 an intricate complex different in composition and with activities 

 peculiar to it, but co-operating with the reticulated mass and 

 fluid constituents. Within late years the structure of the nucleus 

 has been studied with great care. It is found to consist of a 

 membrane, which separates it from the surrounding cell sub- 

 stance, but this membrane is a variable characteristic, for it is 

 sometimes absent, and usually disappears as a preliminary to 

 subdivision. The nucleus, too, has been shown to contain dis- 

 tinct substances. There is a network, or framework, of the most 

 delicate nature in the nuclear cavity, to which the name " linin '' 

 has been given ; there is a nuclear sap, and a distinct proteid 

 substance which is the preponderating material both in quantity 



