1917] 
FREIBERG—MOSAIC DISEASES 219 
This may be hard to understand, but that similar phenom- 
ena do occur is an established fact. It has been demonstrated 
in animal physiology as well as in plant physiology. Abder- 
halden and his co-workers have found that if, for example, 
native protein, proteoses, or peptones are introduced parent- 
ally into an organism, enzymes normally not present in the 
blood will be formed (Underhill, 75). The proteolytic 
enzymes produced hydrolyze the compounds to amino acids 
which are then absorbed from the blood stream by the tissues. 
When hydrolysis of the compounds has been completed, the 
enzymes disappear again, but will be reformed upon the in- 
jection of more of the proteinaceous substances. Knudson 
(713) found that tannase is not produced by Aspergillus niger 
nor by certain species of Penicilliwm if tannic acid or its 
decomposition product, gallie acid, is omitted from the nu- 
trient solution. The amount of tannase produced increases 
in accordance with the concentration of the acids. Many other 
examples might be cited, all of them illustrating the same 
point. 
If the mosaic enzyme acts upon a compound present in the 
healthy plant, or if in the process of photosynthesis it deter- 
mines the formation of certain compounds, we can easily con- 
ceive how the presence of some of the end products or interme- 
diate produets may stimulate the formation of more of the 
enzyme. We must remember that after the enzyme has once 
been introduced into the plant, it plays a part in, and in fact 
becomes a part of, the metabolism of the plant. This fact be- 
comes obvious when we consider the malformations and the 
large amount of ‘‘infective principle’’ that the substance gives 
rise to when injected into normal plants. 
These interpretations are entirely in accord with the funda- 
mental principles upon which all our scientific conceptions in 
pathology and biology are based. The continued formation 
of the mosaic enzyme when once introduced into a healthy 
plant has been accounted for on purely physiological grounds. 
It is of course true that self-reproduction is a characteristic 
of living things, but this must not be confused with the repro- 
duction of chemical compounds, including enzymes, in a highly 
