MAKING A HOME FOR LIFE 215 
For, without going very deeply into the subject, 
it is clear that water was a precursor of life, just as 
it now is an essential concomitant of all vital 
activity. Professor Henderson has worked out its 
appreciation. “ Water can dissolve a larger variety 
of substances in greater concentration than any 
other liquid”; “an enormous quantity of heat is 
necessary in order completely to evaporate away a 
lake or pond, and a smaller, but still very large, 
quantity must be given off before such a body of 
water can freeze throughout its whole extent”; 
the well-known anomalous expansion of fresh water 
near the freezing-point conserves liquid water and 
the life in it. And what shall we say of its capacity 
for hydrolytic cleavage, or of the mobility of its 
molecules, so important in bodily functions? 
But just as water necessarily appeared upon the 
earth when the times were ripe, so carbon dioxide 
was as necessarily present as a primary constituent 
in the air, and the relations of the two made for 
progress. For the law of the solubility of carbon 
dioxide in water is such that at temperatures con- 
sistent with the presence of a hydrosphere “ it must 
always be somewhat evenly distributed between 
the air and the waters of the globe. Water can 
never wash the carbonic acid out of the air, nor the 
extract it from the water.” Moreover, the pres- 
ence of carbonic acid in the rain enabled the waters 
of the earth to mobilize in moderation the resources 
locked up in minerals. 
‘The origin of living organisms upon the earth 
