On chemical changes in their relation to micro-organisms / E. Frankland.

  • Frankland, Edward, 1825-1899.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: On chemical changes in their relation to micro-organisms / E. Frankland. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    brought about in a somewhat mysterious way. Superficially con- sidered, these classes appear to be nearly allied, but on closer study they are found to be essentially different. In the first place, alt^ugh a comparatively small amount of a soluble ferment can produce a chemical change in a large mass of matter, its action is limited; whereas there is no such limit to the action of an organised ferment. Thus the distiller finds that it is necessary to add 18 per cent, of malt in mashing, in order to convert the whole of the stai’ch of the unmalted grain into sugar. But a single yeast cell, in an albuminous liquid, will bring about the con- version of an unlimited amount of sugar into alcohol. Secondly, soluble ferments are unaffected in their activity by chloroform or compressed air, whilst these reagents at once arrest the changes produced by micro-organisms. Thirdly, the changes effected by soluble ferments can, with scarcely an exception, be easily brought about by purely chemical means, whilst those dependent upon the presence of micro-organisms have, with one or two exceptions, never been directly effected by other non- vital means. I have also hazarded the proposition that there is no break in the continuity of chemical functions between micro-organisms and the higher forms of animal life. Both alike owe their vitality to the liberation of the energy stored in their food, and both go through a cycle of existence and then lose their vitality. It is true that there are apparently certain sharp distinctions between them. Thus the enormous fecundity of micro-organisms and their tremendous appe- tites (on the assumption that all the changed matter passes through their bodies) seem to separate them from the higher orders of animals. But this distinction is only comparative. Thus, in regard to fecundity, the power of multiplication gradually increases as the animal descends in the scale of organisation. There are, of course, exceptions, but this is the rule. The sheep produces only one or two lambs annually. The hei’ring in the same time mul- tiplies itself many thousand fold, whilst the aphis produces young at such a rate, that a single specimen would, if all its progeny lived, produce in three months a weight of aphides greater than that of the whole contemporary human race. And, as to appetite, voracity is greatest in the lowest organisms. A sheep or a cow consumes about one-sixth of its own weight in 24 hours; an earthworm, a caterpillar, or a silkworm many times its own weight. The yeast organism must, therefore, taking into account its position in nature, be considered decidedly abstemious, inasmuch as it only consumes two-fifths of its own weight of sugar in the course of 24 hours. Moreover, it must be borne in mind that the sheep converts most of its food into carbonic