302 GPJNERAL PHYSIOLOGY 



3. Preyar's Theory of the Continuity of Life 



By considerations of another kind, Preyer ('80) has arrived at 

 a theory regarding the derivation of life which is opposed to the 

 theories both of spontaneous generation and of cosmozoa. 



Preyer cannot accept the idea of spontaneous generation for 

 the following reasons. If it be assumed that at some one time in 

 the earth's development living substance has arisen spontaneously 

 from lifeless substance, it must be claimed that this is pos- 

 sible even now. But the failure of the innumerable experi- 

 ments directed toward this problem has made it in the highest 

 degree improbable. On the other hand, the supposition that 

 spontaneous generation was possible only once in the primeval 

 past, but now no longer occurs, is likewise improbable; "for the 

 same conditions that are essential for the maintenance of life and 

 are now realised, must necessarily have been realised also at the 

 time of the supposed origin of living from inorganic bodies ; 

 otherwise, the product of spontaneous generation would not have 

 been able to continue living." In other words, if spontaneous 

 generation were once possible, it is difficult to see why it is not 

 possible now. 



Preyer is likewise not able to accept the theory of cosmozoa, 

 because he sees in it not a solution, but only a postponement of 

 the problem, i.e., a shifting of it from the earth to some other 

 world, the problem itself, however, always remaining. 



Proceeding from the inductive fact that organisms are always 

 derived from other organisms similar to them, that thus far 

 observation has never been able to establish the origin of any 

 organism without a parent, Preyer raises the question whether 

 the problem of spontaneous generation may not rest upon a false 

 conception, when it demands that living substance shall at some 

 time have originated iron:i lifeless substance. Must it not rather 

 be formulated in the reverse order : has lifeless originated from 

 living substance ? Organisms are always derived from other 

 living organisms ; but inorganic, lifeless substance is continually 

 being derived from both lifeless substance and living organisms, 

 either being excreted from the latter as dead matter or remaining 

 after their death. In contrast, therefore, to the doctrine of spontane- 

 ous generation, Preyer puts forward the theory that living substance 

 is the primary thing, and that lifeless substance is derived from 

 it secondarily by excretion.^ He thus demands that continuity in 

 the derivation of living substance has never been broken. " Who- 

 ever interrupts the series of successive generations of organisms bj^ 

 the introduction of a generation without previous parentage ; in 

 other words, whoever denies the continuity of life is arbitrary." 



1 Cf. p. 121. 



