368 THE EVOLUTION THEORY 



and reti'act them again, creep in a particular direction, encyst itself, 

 and so on, for all this presupposes a differentiation of its particles in 

 different directions, and a definite arrangement of them ; and there is 

 in addition the marvellous dividing-apparatus of the nucleus which 

 is not wanting even in the Amoeba. All this again points to 

 a historic evolution, a gradual acquiring and an orderly arrangement 

 of differentiations, and sucli an organism cannot have arisen suddenly 

 like a crystal or a chemical combination. 



Thus we are driven back to the lowest known organisms, and 

 the question now before us is whether these smallest living organisms, 

 which are only visible under the highest powers of the microscope, 

 may be referred to spontaneous generation. But here too the answer 

 is. No ; for although there is no nucleus to be found, and no substance 

 which we can afHrm with any certainty to be composed of primary 

 constituents or idioplasm, we do find distinct traces of a previous 

 history, and not the absolutely simple structure of homogeneous living 

 particles, unarranged in any orderly way, which is all that could be 

 derived from spontaneous generation. It has been shown quite 

 recently that the typhus bacillus possesses an extremely delicate 

 much-branched tuft of flagella, which gives it a tremulous motion, 

 and in the cholera bacillus cortical and medullary substances can be 

 distinguished. Thus even here there is differentiation according to 

 the principle of division of labour, and how numerous must be 

 the minute vital particles of which a substance consists when it can 

 form such fine threads as the flagella just mentioned ! Nageli, who 

 elaborated an analogous train of thought in regard to spontaneous 

 generation, calculated the number of these smallest vital particles (his 

 ' micellse ') which must be contained in a ' moneron ' of 0'6 mm. 

 diameter, if we take its dry substance at lo per cent., and he arrived 

 at the amazing figure of loo billions of vital particles. Even if 

 we suppose the diameter of such an organism to be o-ooo6 mm., it 

 would still be composed, according to this calculation, of a million 

 of these vital particles. 



We have reached, in the course of these lectures, the conviction 

 that minute living units form the basis of all organisms, namely, 

 our ' life-bearers ' or ' biophors.' These must be present in countless 

 multitudes, and in a great number of varieties in the different forms 

 of life, but all agree in this, that they are simple, that is, they are not 

 composed in their turn of living particles, but only of molecules, 

 whose chemical constitution, combination, and arrangement are such 

 as to give rise to the phenomena of life. But they may vary, and 

 on this power depends the possibility of their differentiation, which 



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