Abstract
Periodic variations in the malignancy of a transplantable neoplasm of the rabbit, which have been studied during the last four years, have been correlated with certain meteorological conditions and especially with the actual hours of sunshine. It has been found, that periods of maximum and minimum sunlight corresponding with summer and winter were periods of relatively low malignancy; while the periods of greatest malignancy occurred at times of abrupt and rapid changes in the hours of sunshine corresponding roughly with spring and autumn. 1 , 2 The influence of these factors has been interpreted as operating upon or affecting animal economy, while susceptibility or resistance to disease is considered as a function of the animal organism. This conception is supported by analogous variations in experimental syphilis of the rabbit, and the observation that in normal rabbits rhythmic changes in the mass relationship of practically all organs of the body have been found which have a definite relationship to seasonal changes and prevailing meteorological conditions. 3 While a variety of factors are probably involved in the production of these fluctuations, there appears to be a close relationship with sunlight and, in particular, first with the amount of sunlight as represented by the actual hours of sunshine and, second, with the rate and extent of change in the curve of sunshine. Furthermore, it is of considerable interest that these biological variations take place in the usual animal room with its illumination determined, in the first instance, by prevailing weather conditions and, in the second, by the interposition of window glass through which passes all or most of the sunlight.
In order to test this conception of the relationship between sunlight, and the physical state and functional activities of the animal, experiments were undertaken in which conditions of illumination could be controlled.
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