gS BIOLOGICAL LECTURES. 



¥ 



the cell, each with the power of assimilating, of growing and 

 of multiplying by division.^ 



Perhaps the easiest way of arriving at the conception of 

 the existence of such ultra-microscopic organisms in the cell is 

 attained by separating the cytoplasm from the nucleus in a 

 given cell, say an Amoeba, and dividing each of them into 

 smaller and smaller pieces, as far as our imagination can carry 

 us. "Just as in division of the chemical mass we come to the 

 chemical molecule, the further division of which changes the 

 properties of the substance, so in the continual division of the 

 Amoeba we should come to a stage in which farther division 

 interfered with the physiological action ; we should come to a 

 physiological unit, corresponding to, but greatly more complex 

 than the chemical molecule." ^ Such a physiological unit, 

 Foster suggests, might be called a Soviacidc. This physiologi- 

 cal unit is what Weismann calls the "bearer of vitality," or 

 Biopho?-, because it is the smallest unit which exhibits the 

 primary vital forces., viz, assimilation and metabolism, growth, 

 and multiplication by fission''' This unit is not the chemical 

 molecule, hence it has all the essential characteristics of living 

 organisms, such as assimilation and division, and mere 

 molecules can neither assimilate nor multiply. It is, in fact, 

 the organism itself, with all fundamental attributes of the 

 higher organism; indeed, the reason why a higher organism 

 exhibits these fundamental properties, is, as has already been 

 mentioned, because its component units are endowed with such 

 properties. 



Although it is difficult to define the exact nature and morpho- 

 logical character of the physiological units individually, we can 

 study them collectively in the phenomena of their gronpitigs. 



1 The following are the examples of names recently proposed for the cell-form- 

 ing units, by clitlerent writers: Bioblasts (.\ltmann, 1SS7): r.iiii^ciu's (Hugo de 

 Vries, 1889); Somaculcs (M. Foster, 188S); Ptasoincs (J. Wiesner, 1892); Biophors 

 (Weismann, 1893); IdioMasts (i). Hertwig, 1893). Darwin's 6Vww«^-j, Nageli's 

 MicdliC, .Spencer's Pliysioloi^ical units, IClsberg-IIaeckel's Plastidiiles, Bechamp- 

 Estor's Microzyvuis are already well known. It is important, however, to bear in 

 mind that these names are not always synonymous. 



2 M. Foster; .\ Text-lSook of I'hysiology, 5th edition, pp 5-6. 

 8 A. Weismann; The C'.erm-plasma, pp. 39-40. 



