GENERAL 3 



logical importance so long as the other cells remain alive. The protoplasm 

 is the primary living constituent of the cell ; when it dies the cell is dead ; 

 and when the cells and tissues die, the plant is dead. 



The manifestations of life, when traced back to their ultimate origin, 

 are always found to originate in the protoplasm, an undifferentiated mass 

 of which constitutes the substance of the simplest living elementary 

 organism. Hence one of the tasks of Physiology is to throw light on 

 the manner in which the inherent nature of the protoplasm is responsible 

 for the chemical and physical changes to which it gives rise. From 

 a consideration of the organization of the adult plant, it is evident that 

 each individual protoplast must have a complicated structure : as a matter 

 of fact, the cell-nucleus and the chloroplasts are organs of both general 

 and special importance ; vacuoles and cell-walls, though non-living, are 

 also products of vital activity, and of use to the living parts. The proto- 

 plasm itself must be made up of elements or bioplasts, and these, though 

 invisible with the highest powers of the microscope, are not of any the 

 less importance on that account. It is as impossible to picture a regular 

 continuance of life otherwise than by the co-operation of different organs 

 and biological elements, as it is to imagine a watch, which could still 

 keep time after the removal of certain of the wheels. 



Just as a watch ceases to be a watch when crushed to pieces, though 

 the quality and quantity of the component metals remain the same, so 

 also is the life of any protoplasmic body destroyed when it is crushed, 

 although the resultant mass may contain the same substances, and the 

 same amount of them, as before. This consideration, alone, clearly shows 

 that the most detailed information concerning the substances found in 

 protoplasm will be as insufficient to enable us to elucidate the mystery 

 connected with vital processes, as the most complete chemical knowledge 

 of coal and iron is insufficient to afford an explanation of the steam engine, 

 or of the printing press which the latter may drive. 



The chemical nature of the living organism, with its indissolubly 

 connected chemical and mechanical properties, is of much greater impor- 

 tance than that of a machine ; for in the changes which take place in the 

 self-regulating protoplasmic mechanism, chemical nature and affinities are, 

 in all cases, of fundamental importance. Hence progress in Physiology 

 necessarily goes hand in hand with progress in Chemistry. From 

 a physiological standpoint it is hardly possible, for example, to over- 

 estimate the importance of a complete knowledge of the chemical con- 

 stitution of the proteids, which take so prominent a part in building 

 up the living protoplast, especially in view of the possibility that each 

 particular species may be characterized by a specific variety of living 

 proteid. This need not however necessarily be the case, for the manner 

 in which the building material is correlated and arranged is of equal 



B a 



