702 REPORT—1899. 
Mr. Francis Darwin spoke on stimulus as a factor in the problem, and, without 
dissenting from Professor Ward’s view, called attention to a possible difficulty. 
Dr. G. Harris Morris said that he was interested in the subject under dis- 
cussion from the point of view of the so-called symbiotic fermentations, in which 
moulds and yeasts were concerned. Personally he considered the view of Pro- 
fessor Armstrong, that the first-named organism prepared the way for the second, 
to be the correct one, and he thought that the results of certain experiments which 
he hoped to lay before the Section at a later meeting (see p. 710) would support 
that view. In the fermentations referred to, the function of the mould appeared 
to be entirely that of secreting diastase, which degraded the starch products and 
rendered them fermentable by the yeast. The diastase thus secreted could be 
replaced by malt extract or precipitated diastase with precisely the same result, 
and although the diastase so secreted or added was undoubtedly stimulated by the 
fermentative action of the yeast, yet the phenomenon could not be regarded as an 
instance of true symbiosis. A further proof that the one organism prepared the 
way for the other was to be found in the fact that in the commercial process 
which had been mentioned it was found that the best results were obtained when 
the mould, or diastase secretor, was added twenty-four hours before the yeast or 
fermentative agent. : 
The results of the experiments to which he had previously referred showed the 
supposition that the function of one organism was to remove from the field of 
action products which inhibited the action of the other to be untenable. 
He should also like to correct the view, which appeared to be shared by some 
who had taken part in the discussion, that because the moulds were only able to 
produce a comparatively small amount of alcohol, therefore their saccharifying 
action ceased when the formation of alcohol came to an end. This was by no 
means the case, as experiment showed that the extent to which degradation of the 
starch-products had proceeded was by no means indicated by the amount of 
alcohol formed. 
He also could not agree with Professor van Laer in regarding the action of the 
yeast as that of a parasite, and he did not think that any analogy could be drawn 
with the action in question and that of Mycoderma vini. 
[The President of the Section.—It is a matter of great difficulty to determine 
all the actions and reactions of an organism with its environment even when we 
have to deal with a pure culture living in a medium of the simplest possible 
composition, but the difficulty is enormously increased when it is a question of two 
or more organisms, either of which can influence the other in a variety of ways. 
If we consider the process of Dr. Calmette for the preparation of alcohol from 
starch by the metabiotie agencies of a saccharifying Amylomycete or Aspergillus, 
and a true yeast, we find that the actual amount of hydrolytic action exerted by 
the first organism when working alone is extremely small, but that the mere 
presence of a second organism, the yeast, which has the power of fermenting the pro- 
ducts of starch-hydrolysis as fast as they are formed, enormously intensifies the 
initial saccharification. The fact is generally explained by biologists by assuming 
that the yeast in some mysterious manner stimulates the saccharifying organism to 
secrete a larger amount of diastase. This explanation is a pure assumption which 
cannot be proved or disproved by direct experiment. We may, however, as 
Dr. Morris has shown, produce the same effect under conditions where the 
saccharifying organism is replaced by a small but definite amount of diastase 
which remains constant throughout the experiment. Now it is impossible to 
avoid the conclusion that the chemical processes involved are the same in the two 
cases, and that it is perfectly unnecessary to introduce the explanation of an 
increased secretion of diastase by stimulation when we are considering the case in 
which the two metabiotic organisms are concerned. 
An extension of similar work, especially on the simultaneous action of mixed 
enzymes, each one of which is capable of carrying out its own stage of hydrolysis, 
will, no doubt, ultimately throw considerable light on the metabiotic effect of living 
organisms. ‘Take, for instance, the case of diastase and glucase. The former can 
hydrolyse starch down to maltose but no further, whilst the latter, unable in itself 
