SPONTANEOUS GENERATION AND EVOLUTION : CONCLUSION 367 



Up till now all attempts to discover these conditions have been 

 futile, and 1 do not believe that they will ever be successful, not 

 because the conditions must be so peculiar in nature that we cannot 

 reproduce them, but. above all, because we should not be able to 

 perceive the results of a successful experiment. I shall be able to 

 prove this convincingly without difficult}'. 



If we ask ourselves the question how the living beings wliich 

 might have arisen through spontaneous generation must be consti- 

 tuted, and on the other hand, in regard to what kinds of living forms 

 we can maintain with certainty that they could not have arisen thus, 

 it is obvious that Ave must place on the latter list all organisms which 

 presuppose the existence of others, from which they have been 

 derived. But to this category belong all the organisms which possess 

 a germ-plasm, an idioplasm that we conceive of as composed of primary 

 constituents (Anlarjeii) which have graduall}^ been evolved and 

 accumulated through a long series of ancestors. Thus not only all 

 multicellular animals and plants which reproduce by means of germ- 

 cells, buds, and so forth, l)ut also all unicellular organisms, must be 

 placed in this class. For these last — as we have seen — possess in 

 their nucleus a substance made up of primary constituents, without 

 which the mutilated body is unable to make good its loss, in short, an 

 idioplasm. That this plaj's the same role in unicellular as in multi- 

 cellular organisms we can infer with the greatest certainty from the 

 process of amphimixis, which runs its course in an analogous wa}" in 

 both cases. 



Thus, even though we did not know what Ehrenberg demon- 

 strated in the third decade of last centur}', that Infusorians in an 

 encapsuled state can be l)lown about everywhere, and can even be 

 carried across the ocean in the dust of the trade-Avinds, to re-aAvaken 

 to life whereA^er they fall into fresh water, Ave should still not haA'e 

 remained at the standpoint of LeuAA^enhoek, Avho regarded Infusorians 

 as having arisen through spontaneous generation. They cannot arise 

 in this Avay, nor can they have done so at any time, because the}' 

 contain a substance made up of primary constituents, which can only 

 be of historic origin, and cannot therefore haA^e arisen suddenlj- after 

 the manner of a chemical combination. 



The same is true of all the unicellular organisms, CA'en of those 

 Avhich are much more simple in structure than the Infusorians, Avhose 

 differentiation into cortical and medullary substances, oral and anal 

 openings, complex arrangements of cilia and much else, betokens 

 a hio'h degree of differentiation in the cell. But even the Amoeba is 

 only apparently simple, for otherwise it could not send out processes 



