250 Proceedings of the Royal Physical Society. 
general theory was that of Patrick Geddes. This was first 
sketched in a paper read before the Royal Society of Kdin- 
burgh, developed in the articles “ Reproduction” and “Sex” 
in the Encyclopedia Britannica, and finally elaborated in the 
“Evolution of Sex” (London, 1889) by Geddes and Thomson. 
Since the publication of this work, which, in spite of the 
imperfections of a pioneer essay, has had the effect of stimu- 
lating research and discussion, several criticisms and fresh 
theories have been advanced. It is with a few of these, and 
with the general thesis of the “Evolution of Sex,” that we 
have here to do. 
3. GENERAL THEORY OF METABOLISM.—As a necessary 
preliminary, we must take account of the modern concep- 
tion of metabolism. 
So evidently is an organism a system adapted for receiving 
and transforming matter and energy, that the general idea 
of waste and repair has never been far from the minds of 
physiologists. One of the first to make this general idea 
more precise was De Blainville, who described vitality “as 
a twofold internal movement of composition and decom- 
position.” After a time, Claude Bernard—a pioneer in 
the physiology of protoplasm—distinguished “ disassimilating 
combustion and assimilating synthesis.” 
Of recent years various researches and _ speculations, 
especially those of Hering and Gaskell, have led physiologists 
to yet more precise statements in regard to metabolism—in 
some cases perhaps more precise than the known facts warrant. 
Let us carefully notice some of the uncertainties :— 
(a) We do not know whether protoplasm or the living 
matter is one complex substance or a mixture of substances, 
nor within what limits its nature may vary in different 
organisms, in different tissues, or at different times. 
(6) We do not know whether, as Prof. Michael Foster 
suggests, the protoplasm of a cell is, as it were, the centre of 
the metabolic processes, being constantly made and unmade, 
breaking down into waste products, and being built up from 
food; or whether it is, as Prof. Burdon Sanderson suggests, 
a relatively stable stuff, which acts like a ferment on 
adjacent less complex material, now promoting construction, 
and again disruption. 
