35 
] 79*] i jl th* Organic World. 
ese inward factors we know as yet nothing. Nor can 
2 even hope to begin their study till we have first traced 
it and eliminated the workings of the external agencies 
Liich are simpler in themselves, and whose general 
Laradler we have had the opportunity of learning from the 
lenomena of inorganic nature. When this task is once 
complished we shall then find certain “ residual pheno- 
ena ” not to be accounted for by the outward factors above 
entioned, and from these phenomena we may hope to 
gue back to their unknown and doubtless exceedingly com- 
icated causes. 
But very much still remains to be done before we can 
cide with certainty what part is played by such external 
t'ces. 
The functions of electricity have indeed not been dis- 
carded. In semi-scientific circles it fills the post which 
pular tradition once allotted alternately to Michael Scott 
d to the devil — doing duty, namely, as the originator 
everything unaccountable. The influence of light 
d of heat upon organic beings has been investigated 
th much care, and though the task is far from com- 
ste, yet valuable results have been reached. Above all 
has been established that certain limits of temperature 
ist, above and below which all our experience declares life 
be impossible. All organisms, as we find them upon our 
)be, consist of a combination of solids and liquids. But 
low a certain degree of heat the liquid constituents become 
lidified, and thus are rendered incapable of playing their 
rt in the vital process. If such solidification is temporary 
may involve merely a suspension of animation. Above a 
rtain temperature both liquids and solids would be either 
latilised or resolved into their inorganic constituents ; 
nee it follows that the chemical composition of every 
ganism must stand in a certain relation to the thermic 
nditions of the world it inhabits. Very similar is the case 
regards light, its total absence and its excess being alike 
[favourable to the welfare of plants and animals. 
But the effects of gravitation in its several manifesta- 
>ns seem scarcely to have received the attention which 
ey merit. Yet that this all-embracing force must have 
*t its impress upon the organic world, no less than upon 
sless matter, can scarcely require any formal demon - 
ration. 
For what is an animal ? If we take as the type the 
ghest organism known to us, the reply must be — a thinking 
D3 
