. General physiology; an outline of the science of life. 402 GENERAL PHYSIOLOGY ally (Fig. 187), it can easily be demonstrated that this jumping movement is not a thermal effect of light, but is caused chiefly by the blue and violet rays, and, therefore, the rays that are least effective thermally. The same effect can be produced by heat-rays, but ordinary daylight is not sufficient for this ; it requires sunlight of considerable intensity, such as can be obtained by the concentra- tion of direct sunlight by means of a concave mirror. As regards the motion of cross-striated muscles, no instanc
. General physiology; an outline of the science of life. 402 GENERAL PHYSIOLOGY ally (Fig. 187), it can easily be demonstrated that this jumping movement is not a thermal effect of light, but is caused chiefly by the blue and violet rays, and, therefore, the rays that are least effective thermally. The same effect can be produced by heat-rays, but ordinary daylight is not sufficient for this ; it requires sunlight of considerable intensity, such as can be obtained by the concentra- tion of direct sunlight by means of a concave mirror. As regards the motion of cross-striated muscles, no instance is thus far known in which light has exerted an influence upon it with certainty. Nevertheless, some time ago Steinach ('92) showed that certain smooth muscle-fibres can be made to contract by light stimuli. In iishes and Amphibia the sphincter iridis, a muscle which in contraction narrows the pupil of the eye, is, as Steinach found, composed of smooth muscle-fibres which contain a brown pigment. These fibres are stimulated by light directly, without the. Fig. 187.—Spectra of various media ; 1, of a red glass ; 2, of a cobalt glass ; 3, of a green glass ; 4, of a solution of potassium bichromate ; 5, of an ammoniacal solution of a cupric salt. mediation of the central nervous system; this is proved by the fact that even the excised muscle can by illumination be made to contract. Just as in many cases contraction-movements are caused by light, the peculiar motion of the Biatomece can be influenced in a certain sense by the same stimulus. As Engelmann ('82) has found, this ceases when the organisms are put into a dark chamber and oxygen is excluded. But it immediately begins again, when light is allowed to act upon them. This phenomenon, as Engelmann .showed, is due to the fact that, with the exclusion of oxygen, the oxygen necessary to the motion of the Biatomece is soon consumed. If the latter be put into darkness, their movements immediately cease; if they be brought into
Size: 2718px × 919px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookauthorverwornmax18631921, bookcentury1800, bookdecade1890
