
SOME MODERN VIEWS 29 
‘solely under similar influences, and yet they con- 
sidered themselves justified in supposing that natural 
causes are now no longer able independently to 
initiate this living matter, or protoplasm, as it is 
termed. 
Professor Tyndall also took the same kind of 
view. Though he affirmed in the most unhesitating 
language the ultimate similarity between crystalline 
and living matter, and held that all the various 
structures by which the two kinds of matter may be 
represented are equally the “results of the free play 
of the forces of the atoms and molecules” entering 
into their composition, yet he too would have 
us believe that, while differences in degree of 
molecular complexity alone separate living from 
not-living matter, the physical agencies which 
freely occasion the growth of living matter are 
now incapable of causing its origination. 
The opinions of these four leaders in science con- 
cerning the question of “spontaneous generation,” 
profoundly influenced public opinion in this country 
during the latter third of the last century. 
They were doubtless influenced, as many others 
have been, in the first place, by two general con- 
siderations which, taken together, seemed to carry 
great weight. 
(1) The exposure of the untruth of certain old 
and crude doctrines concerning ‘spontaneous 
generation,” prevalent more or less from the time of 
Aristotle down to the first third of the last century ; 
and the fact that the belief in this mode of genera- 
tion has been successively driven, with increasing 
