236 MUSCULAR FIBRES IN POLARISED LIGHT, BY E. BRUCKE. 



Prof. C. Bceck,* of Christiania, who was the first that applied 

 the polarising microscope to the investigation of animal and 

 vegetable tissues; and no other intelligible explanation has 

 since this period been advanced of the phenomena observed. 



The next question to determine is, whether the entire sub- 

 stance of the muscular fibres possesses an equal power of 

 double refraction, or whether it is possible to distinguish 

 doubly refracting from isotropal parts. If sufficiently high 

 magnifying powers are employed, and the observations be 

 made on animals which have large sarcous elements, amongst 

 which our large water-beetle, the Hydrophilus piceus, is the 

 best, it will be immediately seen that only the sarcous elements 

 are doubly refracting, and that the intervening material which 

 separates them from one another is isotropal; for it remains 

 dark in the dark field of the crossed Nicol's prisms, in what- 

 ever azimuth the muscular fibre to which it forms a part may be 

 placed ; it is just as dark in those muscular fibres which form 

 an angle of 45 with the polarising planes of the prisms, as in 

 those which make an angle of or of 90 with those planes. 



This becomes still more evident if a water-beetle be killed by 

 immersion in strong alcohol, and after a few days' maceration 

 the muscles of one of its thighs be placed in oil of turpentine, 

 and finally in Canada balsam. Owing to the high refracting 

 index of the balsam the muscular fibres appear in ordinary 

 light very pale and transparent, and all the stronger shadows 

 vanish ; but on this very account all the phenomena caused by 

 double refraction appear with corresponding distinctness under 

 the polarising microscope. But in what way are the sarcous 

 elements doubly refractile ? Are they positive or negative ? 

 Are they uniaxial or biaxial ? 



If a transverse section of the muscle hardened in spirit be 

 thoroughly impregnated with Canada balsam, and examined 

 with the polarising apparatus, it will be found that as it is 

 turned round the axis of the instrument a portion of the cut 



* Transactions of the Scandinavian Society of Naturalists in Gotheborg 

 in 1839, and in Copenhagen in 1840. Report on the progress of Anatomy 

 and Physiology in Scandinavian Literature in the years 1840 1843, by 

 Ad. Hannover, in J. Moiller's Archivfur Anatomie u. Physiologie^ 1844. 



