Darwin and Modern Science [181]
- wiskotti elymi
klymene merrifieldi atalanta - merrifieldi klymene
weismanni porima prorsa - porima weismanni
The reader will notice that the aberrations produced at a very low temperature (from 0 to -20 deg C.) are absolutely identical with the aberrations produced by exposing the pupae to extremely high temperatures (42 to 46 deg C.). Moreover the aberrations produced by a moderately low temperature (from 0 to 10 deg C.) are identical with the aberrations produced by a moderately high temperature (36 to 41 deg C.)
From these observations Fischer concludes that it is erroneous to speak of a specific effect of high and of low temperatures, but that there must be a common cause for the aberration found at the high as well as at the low temperature limits. This cause he seems to find in the inhibiting effects of extreme temperatures upon development.
If we try to analyse such results as Fischer's from a physico-chemical point of view, we must realise that what we call life consists of a series of chemical reactions, which are connected in a catenary way; inasmuch as one reaction or group of reactions (a) (e.g. hydrolyses) causes or furnishes the material for a second reaction or group of reactions (b) (e.g. oxydations). We know that the temperature coefficient for physiological processes varies slightly at various parts of the scale; as a rule it is higher near 0 and lower near 30 deg. But we know also that the temperature coefficients do not vary equally from the various physiological processes. It is, therefore, to be expected that the temperature coefficients for the group of reactions of the type (a) will not be identical through the whole scale with the temperature coefficients for the reactions of the type (b). If therefore a certain substance is formed at the normal temperature of the animal in such quantities as are needed for the catenary reaction (b), it is not to be expected that this same perfect balance will be maintained for extremely high or extremely low temperatures; it is more probable that one group of reactions will exceed the other and thus produce aberrant chemical effects, which may underlie the colour aberrations observed by Fischer and other experimenters.
It is important to notice that Fischer was also able to produce aberrations through the application of narcotics. Wolfgang Ostwald has produced experimentally, through variation of temperature, dimorphism of form in Daphnia. Lack of space precludes an account of these important experiments, as of so many others.
IV. THE EFFECTS OF LIGHT.
At the present day nobody seriously questions the statement that the action of light upon organisms is primarily one of a chemical character. While this chemical action is of the utmost importance for organisms, the nutrition of which depends upon the action of chlorophyll, it becomes of less importance for organisms devoid of chlorophyll. Nevertheless, we find animals in which the formation of organs by regeneration is not possible unless they are exposed to light. An observation made by the writer on the regeneration of polyps in a hydroid, Eudendrium racemosum, at Woods Hole, may be mentioned as an instance of this. If the stem of this hydroid, which is usually covered with polyps, is put into an aquarium the polyps soon fall off. If the stems are kept in an aquarium where light strikes them during the day, a regeneration of numerous polyps takes place in a few days. If, however, the stems of Eudendrium are kept permanently in the dark, no polyps are formed even after an interval of some weeks; but they are formed in a few days after the same stems have been transferred from the dark to the light. Diffused daylight suffices for this effect. Goldfarb, who repeated these experiments, states that an exposure of comparatively short duration is sufficient for this effect, it is possible that the light favours the formation of substances which are a prerequisite for the origin of polyps and their growth.
klymene merrifieldi atalanta - merrifieldi klymene
weismanni porima prorsa - porima weismanni
The reader will notice that the aberrations produced at a very low temperature (from 0 to -20 deg C.) are absolutely identical with the aberrations produced by exposing the pupae to extremely high temperatures (42 to 46 deg C.). Moreover the aberrations produced by a moderately low temperature (from 0 to 10 deg C.) are identical with the aberrations produced by a moderately high temperature (36 to 41 deg C.)
From these observations Fischer concludes that it is erroneous to speak of a specific effect of high and of low temperatures, but that there must be a common cause for the aberration found at the high as well as at the low temperature limits. This cause he seems to find in the inhibiting effects of extreme temperatures upon development.
If we try to analyse such results as Fischer's from a physico-chemical point of view, we must realise that what we call life consists of a series of chemical reactions, which are connected in a catenary way; inasmuch as one reaction or group of reactions (a) (e.g. hydrolyses) causes or furnishes the material for a second reaction or group of reactions (b) (e.g. oxydations). We know that the temperature coefficient for physiological processes varies slightly at various parts of the scale; as a rule it is higher near 0 and lower near 30 deg. But we know also that the temperature coefficients do not vary equally from the various physiological processes. It is, therefore, to be expected that the temperature coefficients for the group of reactions of the type (a) will not be identical through the whole scale with the temperature coefficients for the reactions of the type (b). If therefore a certain substance is formed at the normal temperature of the animal in such quantities as are needed for the catenary reaction (b), it is not to be expected that this same perfect balance will be maintained for extremely high or extremely low temperatures; it is more probable that one group of reactions will exceed the other and thus produce aberrant chemical effects, which may underlie the colour aberrations observed by Fischer and other experimenters.
It is important to notice that Fischer was also able to produce aberrations through the application of narcotics. Wolfgang Ostwald has produced experimentally, through variation of temperature, dimorphism of form in Daphnia. Lack of space precludes an account of these important experiments, as of so many others.
IV. THE EFFECTS OF LIGHT.
At the present day nobody seriously questions the statement that the action of light upon organisms is primarily one of a chemical character. While this chemical action is of the utmost importance for organisms, the nutrition of which depends upon the action of chlorophyll, it becomes of less importance for organisms devoid of chlorophyll. Nevertheless, we find animals in which the formation of organs by regeneration is not possible unless they are exposed to light. An observation made by the writer on the regeneration of polyps in a hydroid, Eudendrium racemosum, at Woods Hole, may be mentioned as an instance of this. If the stem of this hydroid, which is usually covered with polyps, is put into an aquarium the polyps soon fall off. If the stems are kept in an aquarium where light strikes them during the day, a regeneration of numerous polyps takes place in a few days. If, however, the stems of Eudendrium are kept permanently in the dark, no polyps are formed even after an interval of some weeks; but they are formed in a few days after the same stems have been transferred from the dark to the light. Diffused daylight suffices for this effect. Goldfarb, who repeated these experiments, states that an exposure of comparatively short duration is sufficient for this effect, it is possible that the light favours the formation of substances which are a prerequisite for the origin of polyps and their growth.