324 Evolution and Adaptation 
as its powers of resistance are concerned it is a very differ- 
ent being. 
In regard to the perpetuation of the advantages gained by 
means of this power of adaptation, it is clear in those cases 
in which the young are nourished during their embryonic 
life by the mother, that, in this way, the young may be 
rendered immune to a certain extent, and there are instances 
of this sort recorded, especially in the case of some bacterial 
diseases. Whether this power can also be transmitted through 
the egg, in those instances in which the egg itself is set free 
and development takes place outside the body, has not been 
shown. In any case, the effect appears not to be a perma- 
nent one and will wear off when the particular poison no 
longer acts. It is improbable, therefore, that any permanent 
contribution to the race could be gained in this way. Adap- 
tations of this sort, while of the highest importance to the 
individual, can have produced little direct effect on the evolu- 
tion of new forms, although it may have been often of para- 
mount importance to the individuals to be able to adapt 
themselves, or rather to become able to resist the effect of 
injurious substances. The important fact in this connection 
is the wonderful latent power possessed by all animals. So 
many, and of such different kinds, are the substances to 
which they may become immune, that it is inconceivable 
that this property of the organism could ever have been 
acquired through experience, no matter how probable it may 
be made to appear that this might have occurred in certain 
cases of fatal bacterial diseases. And if not, in so many 
other cases, why invent a special explanation for the few 
cases ? 
We may defer the general discussion of the réle that 
external factors have played in the adaptation of organisms, 
until we have examined some of the theories which attribute 
changes to internal factors. The idea that something innate 
in the living substance itself has served as the basis for evolu- 
