UNPROVEN, NOT IMPOSSIBLE 9 



Many investigators, and amongst them C. NAGELI (I.), assumed that these 

 lowest forms really exist, although undiscovered at present, and in his important 

 and highly suggestive work on the Theory of Descent which also contains a 

 fine chapter on " the limits of knowledge in natural science " this author 

 touches upon the question under consideration. He calls these presumptive 

 connecting links Probien (pre-existing), on the ground of their being the pre- 

 decessors of all known forms of living beings. Such a Probion resulting from 

 spontaneous generation would be " merely a drop of homogeneous structureless 

 plasma, devoid of any definite form and composed of albuminates, associated 

 only with the compounds necessary for nutrition." 



"We must assume" says de Bary "that organisms must at one time 

 have originated from organisable but unorganised substances, without pro- 

 genitors. ... To prove such a primary creation of a living being is of the 

 highest interest, and exercises the same fascination on the investigator as the 

 expectation of the homunculus in the phial did on the alchemist. The expe- 

 rience of centuries has, however, shown that the homunculus when it actually 

 appeared was simply a small imp which had been secretly passed into the flask 

 by sleight of hand. . . . Therefore admitting all imaginable possibilities 

 the law, based on experience, of origin from ancestors, corresponds with the 

 enlightened state of our knowledge, and this is the starting-point that must be 

 taken in a work which has to deal with the exact sciences." 



