The Problem of Adaptation 27 
thatits integrity is maintained. Most machines have no such 
regulative power, although, in a sense, the fly-wheel of an 
engine regulates the speed, and a water-bath, with a ther- 
mostat, regulates itself to a fixed temperature; but even this 
comparison lacks one of the essential features of the regula- 
tion seen in organisms, namely, in that the regulation does 
not protect the machine from injury. It may be claimed, 
however, that the safety valve of an engine does fulfil this 
purpose, since it may prevent the engine from exploding. 
Here, in fact,-we do find better grounds for comparison, but, 
when we take into account the relation of the regulations in 
the organism to all the other properties of the organism, 
we see that this comparison is not very significant. The 
most essential difference between a machine and an organism 
is the power of reproduction possessed by the latter, which is 
absent in all machines. Here, however, we meet with a 
somewhat paradoxical relation, since the reproductive power 
of organisms cannot be looked upon as an adaptation for the 
continuation of the individual, but rather for the preservation 
of a series of individuals. Hence, in this respect also, we 
cannot profitably compare the individual with a machine, but 
if we make any comparison we should compare all the indi- 
viduals that have come from a single one with a machine. 
In this sense the power of reproduction is a sort of racial 
regulation. A comparison of this sort is obviously empty of 
real significance. 
The regenerative power of the organism, by means of 
which it may replace a lost part, or by means of which a 
piece may become a new whole, is also something not 
present in machines. 
In using a machine for comparison we should not leave 
out of sight the fact that machines are themselves the work 
of organisms, and have been made for some purpose useful 
to the organism. They may perform the same purpose for 
which we would use our own hands, for they differ from 
