ADDRESS. 15 



along with the radiations, a, characteristic appearance when the process of 

 nuclear division is about to begin. 



One can scarcely regard the presence of so remarkable an appearance 

 as the achromatic figure without associating with it an important function 

 in the economy of the cell. As from the centrosome at the pole of 

 the spindle both sets of radiations diverge, it is not unlikely that it acts 

 as a centre or sphere of energy and attraction. By some observers the 

 radiations are regarded as substantive fibrillar structures, elastic or even 

 contractile in their propei'ties. Others, again, look upon them as morpho- 

 logical expressions of chemical and dynamical energy in the protoplasm of 

 the cell body. On either theory we may assume that they indicate an 

 influence, emanating, it may be, from the centrosome, and capable of 

 being exercised both on the cell plasm and on the nucleus contained 

 in it. On the contractile theory, the radiations which form the body 

 of the spindle, either by actual traction of the supposed fibrillas or by 

 their pressure on the nucleus which they surround, might impel during 

 karyokinesis the dividing chromosome elements towards the poles of the 

 spindle, to form there the daughter nuclei. On the dynamical theory, 

 the chemical and physical energy in the centrosome might influence the 

 cell plasm and the nucleus, and attract the chromosome elements of the 

 nucleus to the poles of the spindle. The radiated appearance would 

 therefore be consequent and attendant on the physico-chemical activity 

 of the centrosome. One or other of these theories may also be applied to 

 the interpretation of the significance of the polar radiations. 



Cell Plasm. 



In the cells of plants, in addition to the cell wall, the cell body and 

 the cell juice require to be examined. The material of the cell body, or 

 the cell contents, was named by von Mohl (1846) protoplasm, and consisted 

 of a colourless tenacious substance which partly lined the cell wall 

 (primordial utricle), and partly traversed the interior of the cell as deli- 

 cate threads enclosing spaces (vacuoles) in which the cell juice was con- 

 tained. In the protoplasm the nucleus was embedded, Nageli, about the 

 same time, had also recognised the difference between the protoplasm and 

 the other contents of vegetable cells, and had noticed its nitrogenous com- 

 position. 



Though the analogy with a closed bladder or vesicle could no longer be 

 sustained in the animal tissues, the name ' cell ' continued to be retained 

 for descriptive purposes, and the body of the cell was spoken of as a 

 more or less soft substance enclosing a nucleus (Leydig). In 1861 Max 

 Schultze adopted for the substance forming the body of the animal cell 

 the term 'protoplasm.' He defined a cell to be a particle of protoplasm 

 in the substance of which a nucleus was situated. He regarded the 

 protoplasm, as indeed had previously been pointed out by the botanist 

 linger, as essentially the same as the contractile sarcode which 



