5 5 8 Ward . — Symbiosis. 
other algae will appreciate the significance of this one with 
Spirogyra. 
However feeble the evidence may be, we can at least say, 
then, that there is some evidence in support of the hypothesis 
that one symbiont may stimulate another by excreting some 
body which acts as an exciting drug to the latter — just as 
truly as certain drugs act as stimulants to some cell or organ 
of a higher animal, and no doubt in a fundamentally similar 
manner (44 b). It will be noted that such drugs are frequently 
excreta from vegetable cells. 
But there is another, perhaps more indirect way in which 
one symbiont may enhance the activity of another. It has 
long been known that the accumulation of the products of 
metabolism of a cell tend to inhibit the activity of that cell, 
and that if by any means we can destroy or remove the 
metabolite as it is formed, the cell concerned can go on 
working. Similarly with ferments, and even with enzymes, 
the accumulation of the products gradually inhibits the action, 
as Tammann (45) showed in the case of Amygdalin and 
emulsin, and Brown and Morris (46) and Lea (47) in the 
case of starch and diastase, to mention two illustrations only. 
Now suppose we have two organisms A and B living 
in symbiosis, and suppose that A is capable of hydrolysing 
starch by the excretion of diastase, while B removes the 
product of hydrolysis, by fermenting the sugar as fast as it is, 
formed ; in this case there is every reason to expect that 
A will push its hydrolysing action to the utmost, not only 
because it is of advantage to A to be relieved of the inhibiting 
sugar, but because the diminution of the sugar re-acts as 
a stimulus to the secretion of more enzyme. 
There is yet another point to be considered. Katz, in 
1898 (48), published some results confirming in many points 
the discoveries of Wortmann (49), Brown and Morris (50), and 
others, that Fungi, Bacteria, embryos, and other enzyme- 
secreting organisms not only vary the extent and kind of 
enzyme secreted, but can be stimulated to vary the enzyme 
according to the quantity or quality of food materials at hand. 
