210 Proceedings of the Eoyal Society 
that already indicated, must act through the organism and the 
organic fluids which take their first origin in this manner. 
The character of nutrition throughout organic nature is then 
dwelt on, with the purpose of showing that it is everywhere under 
the control of more or less perfect organic (physiological) atoms ; 
that even reproduction of species is nutrition of a more special 
kind, the organic atoms supplied by each sex being thrown off only 
when the individual or individuals whence they are derived have 
attained a very perfect maturity. 
The maintenance of heat in organic bodies, and particularly in 
animals of perfect type, is next pointed out as probably indicating 
the true nature of the connection between vital agency and the 
physical forces, since in every case the higher temperature has a 
purely physical source, while it is nevertheless under the control 
of vital agency. 
A rapid view is next taken of acts of relation in the animal 
world, as more immediately proving the necessity for a directive 
principle to explain, in any degree, the reference of such acts to 
physical forces. 
Finally, the interference of a directive principle is represented 
as essential to show why vital agency at last puts a limit to its own 
operations, even when the material supplied is in abundance, first 
building up the springs of growth and limiting the size of each 
individual over which it presides, in accordance with the rule of 
the species ; next building up the springs of reproduction earlier in 
the one sex than in the other ; and, lastly, building up the springs 
of life itself, and terminating the career of its own individual 
existence in a manner even less intelligible to finite under- 
standings than any of the most wonderful of its acts of workman- 
ship in the greatest vigour of its power. 
A few passages are then devoted to the exhibition of views taken 
by Carpenter, Leconte, also by Thomson and Tait, in speaking of 
organic phenomena with reference to the correlation of physical 
forces or to the conservation of energy. 
Affinity and aggregation are next reviewed at some length, with 
the view of showing that there is no essential difference between 
affinity in inorganic nature and that affinity which builds up and 
repairs organic structures when the agency of a directive principle 
