NUTRITION . 89 
been manufactured from simpler substances, artificially 
in the laboratory, without the aid of living organisms; 
and they may all be digested artificially in a test-tube, 
also without the aid of living organisms; but, although 
the attempt has often been made, no one has ever suc- 
ceeded in artificially producing even the minutest drop 
of living protoplasm. Only living protoplasm, acting 
directly on non-living matter, can bring about that 
marvellous change. This fact is concisely expressed by 
the Latin phrase, "Omne vivum e vivo" (All life from life). 
87. Biogenesis. That living matter is always descended 
from preceding living matter, and that it never arises 
spontaneously from the non-living is the principle of 
biogenesis. 1 Opposed to this principle is the principle 
of abiogenesis, 2 which 'teaches that living matter may 
originate from non-living without the intervention of 
other living matter. This was formerly quite generally 
believed. Men thought, for example, that putrid meat 
might become transformed directly into the maggots 
(young flies) so often found in it; but we now know that 
maggots in decaying meat always arise from the eggs of 
flies that have previously visited the meat and deposited 
their eggs there. Thanks to the painstaking experiments 
and clear thinking of Redi, Pasteur, Tyndall, and others, 
belief in the principle of biogenesis is now practically 
universal among scientists. 
That living matter could not, under favorable condi- 
tions, originate from non-living matter, or that it did not 
in the beginning, or never does now, cannot, of course, 
1 Biogenesis, from the Greek words bios (/3to j), life, and genesis (ytvais) 
generation. 
1 Abiogenesis. The prefix a (Greek alpha) deprives the remainder of 
the word of its meaning, or reverses the meaning. 
