1889-90.] Dr G. E. C. Wood on Enzyme Action. 
51 
as it usually does for the most part in merely increasing the inter- 
molecular spaces by increasing the mean free path of the molecule 
by means of the enzyme, is presented in such a form that it is taken 
up by the molecule or rather by a part of the molecule until its in- 
tegrity is wrecked and dissociation occurs. Now we have already 
seen that the enzyme is merely a property separable from the proto- 
plasm, hut not differing otherwise from other functions. Each 
enzyme has its optimum temperature, and may not the different 
catalysing powers of the protoplasm of an organism have different 
optimum temperatures ? A series of facts which have been accumu- 
lating for some time must, I think, be explained in this way. We 
find that the pigment bacilli have each an optimum temperature at 
which they produce most readily their pigment, although this does 
not necessarily coincide with that at which they grow most rapidly. 
Thus Prodigiosus grown at the usual temperature of the room, is of 
a striking red colour, hut, when cultivated at the temperature of the 
animal body, it is absolutely colourless.* I had recently occasion to 
* This need not be entirely attributed to the direct influence of the tempera- 
ture on the catalysing processes ; the protoplasm, as we have already seen, 
exhibits a selective action as regards the different substances offered it as food, 
and it maybe that when one process is partially interfered with, a similar 
power may come into play, and this would exaggerate the direct effect of the 
temperature. Correlated with these perhaps only quantitative changes which 
may be catabolic or anabolic in character, the metabolism as a whole may 
become more or less altered, so that the centre of gravity of the organism 
becomes as it were shifted. It is to this, probably, that we must refer the fact 
noted by Schottelius that, when Prodigiosus is grown for a certain time at the 
higher temperature, it loses the faculty of producing its pigment even when 
grown at a lower temperature. In a more recent communication he states 
that, when grown sufficiently long at the lower temperature, the property 
returned, so that we have here an example of that form of “reversion” which 
Romanes has recently so ably discussed. Dallinger has found that Infusoria 
can be gradually accustomed to withstand very high temperatures, and this 
adaptation may be associated with a similar change in the metabolism. The 
“tolerance” which Kossiakoff ( Annales de VInstitut Pasteur , No. 10, 1887) 
has shown that microbes can acquire towards antiseptic agents when previously 
cultivated in more dilute solutions, is to be referred chiefly to the organisms 
becoming gradually accustomed to exist without those “ associations” and 
“ dissociations ” which the chemical substance tends to inhibit, and to a cor- 
responding development of others to take their place. The permanence of this 
new habit of the organism, when grown again under the old conditions, will 
depend on the more or less stable nature of the new combination or complex 
functions which has been evolved. This modification of the organism as a 
whole, which may result from a change in one direction, and is dependent on 
