913 
of Edinburgh, Session 1885 - 86 . 
sarily disproportionate increase of surface implies less opportunity 
for nutrition, respiration, and excretion, and waste thus overtakes, 
balances, and threatens to exceed repair. Three alternatives are 
then possible ; (a) a temporary equilibrium may be established, and 
growth ceases, or (b) the increase of waste may bring about dissolution 
and death, or still more frequently (c) the balance of mass and surface 
may be restored by the division of the cell. 
Now, these facts may be expressed in lower and more definite 
terms. The early growth of the cell, the increasing bulk of con- 
tained protoplasm, the accumulation of nutritive material, corre- 
spond to a predominance of processes which are constructive or 
anabolic. The growing disproportion between mass and surface 
implies a relative decrease of anabolism, while the simple con- 
tinuance of life or metabolism entails a gradually increasing pre- 
ponderance of destructive processes or katabolism. While growth 
continues, the algebraic sum of the protoplasmic process is of course 
+ on the side of anabolism, and growth may thus be defined as the 
preponderance of an anabolic tendency, rhythm, or diathesis. The 
limit of growth, when waste has overtaken and begun to exceed the 
income or repair, corresponds in the same way to the maximum of 
katabolic preponderance consistent with life, in other words, to the 
climax of the katabolic diathesis. It is well known, for instance, 
that cell division occurs especially at night, when nutrition is at a 
standstill, and when there is therefore a relative katabolic prepon- 
derance. 
Nor does this definition of the limit of growth apply only to 
cells, but also, of course, to cell-aggregates. The phenomena of 
growth in the history of tissue and organ, of organism and stock 
alike are expressible in terms of the anabolic and katabolic balance 
above referred to. The average size of the species, the length of its 
life, the advent of the reproduction which marks the beginning of 
death, must submit to be similarly rationalised. The palaeonto- 
logist, even, may be enabled to understand the rationale of that 
attainment of great bulk exhibited by so many of the highest types 
of ancient as well as of modern faunas, and also of the constant 
tendency of such gigantic forms to extinction. 
§ 2. Reproduction (a) Asexual . — It has been noted above that a 
continued surplus of anabolism involves growth, that this growth is 
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