ABSTRACT
Nevertheless it must be admitted that a large and varied mass of data dealing with the effects of temperature on biological processes, some new and many based on observations which were collected for ulterior purposes by other workers, have been shown by Crozier and his co-workers to conform to the equation of Arrhenius with remarkable fidelity. On the basis of these calculations Crozier has urged the possibility of distinguishing between the slowest chemical reactions of a series involved in different biological processes.
As to the legitimacy of attaching much weight to this view, there is still room for divergence of opinion. But one may say that there is good reason for exploring further the correspondence between hypothesis and fact. During a summer’s work at St Andrews, New Brunswick, the author took the opportunity, at the suggestion of Professor Lancelot Hogben, of studying from this point of view the effect of temperature on the rate of the heart beat in three genera of Crustacea, viz.: the Mysids, Thysanoessa and Mictheimysis, and the Euphausid, Meganyctiphanes. Of these three, Mictheimysis is confined to comparatively warmer waters.
The whole animal was placed in a bath of normal medium at the outset of the experiment. The temperature of this was then gradually lowered. The frequency of the cardiac rhythm was observed through the transparent dorsal cuticle with the aid of a binocular microscope, and a stop-watch. Special care was directed to two points in these manipulations. First, the animal was left for five minutes the bath before the counts were made. As these individuals are all relatively small—not more than three-quarters of an inch—this interval was deemed adequate for the adjustment of the body temperature of the experimental animal to that of the surrounding medium. Second, observations were made to control the possibility that the abruptness of the gradient in passing from one temperature to another did not enter into the final result. In a number of experiments a series of observations were made in which successive determinations with diminishing temperature were supplemented by the inverse operation of successive determinations with increasing temperature.
The results are plotted in Figs. 1-3 where the common logarithm of the frequency is plotted against the reciprocal of the absolute temperature. There will be seen to be a pretty close linear agreement within the narrow range of—20 C. to 18° C.; the values of p, given in the figures are calculated graphically on the assumption that a true linear relation exists.
