SPONTANEOUS GENERATION AND EVOLUTION : CONCLUSION 369 



has taken place in more and more diverse ways in the course of 

 phylogeny. They, too, arise in the existing organism, like all vital 

 units, only by multiplication of the biophors already present, but they 

 do not necessarily presuppose a historic origin ; it is conceivable of 

 them, at least as far as their first and simplest forms are concerned, 

 that they may have arisen some time or other through spontaneous 

 generation. In regard to them alone is the possibility of origin 

 through purely chemico-physical causes, without the co-operation of 

 life already existing, admissible. It is only in regard to them that 

 spontaneous generation is not inconceivable. 



We must, therefore, assume that, at some time or other in the 

 history of the earth, the conditions necessary to the development of 

 these invisible little living particles must have existed, and that the 

 whole subsequent development of the organic world must have de- 

 pended upon an aggregation of these biophors into larger complexes, 

 and upon their differentiation within these complexes. 



We shall never be able, then, directly to observe spontaneous 

 generation, for the simple reason that the smallest and lowest living 

 particles which could arise through it, the Biophoridse, are so ex- 

 tremely far below the limits of visibility, that there is no hope of our 

 ever being able to perceive them, even if we should succeed in 

 producing them by spontaneous generation. 



I do not propose to discuss the chemical problem raised by the 

 possible occurrence of spontaneous generation. We have already 

 seen that dead protoplasm, in addition to water, salts, phosphorus, 

 sulphur, and some other elements, chiefly and invariably contains 

 albumen ; an albuminoid substance must, therefore, have arisen from 

 inorganic combinations. No one will maintain that this is impossible, 

 for we continually see albuminoid substances produced in plants from 

 inorganic substances, compounds of carbon and nitrogen ; but under 

 what conditions this would be possible in free nature, that is, outside 

 of organisms, cannot as yet be determined. Possibly we may some • 

 time succeed in procuring albumen from inorganic substances in the 

 laboratory, and if that happens the theory of spontaneous generation 

 will rest upon a firmer basis, but it will not have been experimentally 

 proved even then. For while dead albumen is certainly nearly allied 

 to living matter, it is precisely life that it lacks, and as yet we 

 do not know what kinds of chemical difierence prevail between the 

 dead proteid and the living ; indeed we must honestly confess that it 

 is a mere assumption when we take for granted that there are only 

 chemico-physical diff'erences between the two. It cannot be proved, 

 in the meantime, that there is not another unknown power in the 

 II. B b 



