| Temperature | Time Required for Nineteen Heart-beats in the Embryo of Fundulus | |
|---|---|---|
| °C. | Seconds | |
| 30 | 6. | 25 |
| 25 | 8. | 5 |
| 20 | 11. | 5 |
| 15 | 19. | 0 |
| 10 | 32. | 5 |
| 15 | 61. | 0 |
| 10 | 33. | 5 |
| 15 | 18. | 8 |
| 20 | 12. | 0 |
| 25 | 10. | 0 |
| 30 | 6. | 0 |
Why does each embryo have the same rate of heart-beat at the same temperature in contradistinction to the enormous variability of the same rate in man? The answer is, on account of the elimination of all secondary disturbing factors. In the embryo of Fundulus the heart-beat is a function almost if not exclusively of two variables, the mass of enzymes for the chemical reactions underlying the heart-beat and the temperature. By inheritance the mass of enzymes is approximately the same and in this way all the embryos beat at the same rate (within the limits of the fluctuating variation) at the same temperature. This identity exists, however, only as long as the embryo is relatively quiet in the egg. As soon as the embryo begins to move this equality disappears since the motion influences the heart-beat and the motility of different embryos differs.
In man the number of disturbing factors is so great that no equality of the rate for the same temperature can be expected. Differences in emotions or the internal secretions following the emotions, differences in previous diseases and their after-effects, differences in metabolism, differences in the use of narcotics or drugs, and differences in activity are only some of the number of variables which enter.
4. As stated above the temperature influences practically all life phenomena in a similar characteristic way, e. g., the production of CO2 in seeds[259] and the assimilation of CO2 by green plants.[260] The writer would not be surprised if even the aberrations in the colour of butterflies under the influence of temperature turned out to be connected with the temperature coefficient. The experiments of Dorfmeister, Weismann, Merrifield, Standfuss, and Fischer, on seasonal dimorphism and the aberration of colour in butterflies have so often been discussed in biological literature that a short reference to them will suffice. By seasonal dimorphism is meant the fact that species may appear at different seasons of the year in a somewhat different form or colour. Vanessa prorsa is the summer form, Vanessa levana the winter form of the same species. By keeping the pupæ of Vanessa prorsa several weeks at a temperature of from 0° to 1° Weismann succeeded in obtaining from the summer chrysalids specimens which resembled the winter variety, Vanessa levana.
If we wish to get a clear understanding of the causes of variation in the colour and pattern of butterflies, we must direct our attention to the experiments of Fischer, who worked with more extreme temperatures than his predecessors, and found that almost identical aberrations of colour could be produced by both extremely high and extremely low temperatures. This can be seen clearly from the following tabulated results of his observations. At the head of each column the reader finds the temperature to which Fischer submitted the pupæ, and in the vertical column below are found the varieties that were produced. In the vertical column A are given the normal forms:
TABLE XV
| 0° to -20°C. | 0° to +10°C. | A (Normal Forms) | +35° to +37°C. | +36° to +41°C. | +42° to +46°C. |
|---|---|---|---|---|---|
| ichnusoides (nigrita) | polaris | urticæ | ichnusa | polaris | ichnusoides (nigrita) |
| antigone (iokaste) | fischeri | io | —— | fischeri | antigone (iokaste) |
| testudo | dixeyi | polychloros | erythromelas | dixeyi | testudo |
| hygiæa | artemis | antiopa | epione | artemis | hygiæa |
| elymi | wiskotti | cardui | —— | 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°C.) are absolutely identical with the aberrations produced by exposing the pupæ to extremely high temperatures (42° to 46°C.). Moreover, the aberrations produced by a moderately low temperature (from 0° to 10°C.) are identical with the aberrations produced by a moderately high temperature (36° to 41°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.