78 MUSCULAR TISSUE. 



muscle so treated, a preparation is made on the plate of mica 

 above mentioned, the muscular fibres being teased in such a 

 way that they lie in various directions. If the preparation is 

 now examined in the purple field (obtained as above described), 

 the different colors of the individual muscular fibres are brought 

 out with the greatest distinctness. On rotation of the upper 

 Nicol they undergo changes : if the rotation extends to 90, 

 each color is replaced by its complementary. In a cross section 

 of a muscle (of any animal) hardened in alcohol, and prepared 

 in dammar varnish after steeping in turpentine, the individual 

 fibres show various degrees of illumination. All transitions 

 present themselves between those which are bright between 

 crossed Nicols, and those which are completely invisible; and 

 it is found that the latter are those which are cut in planes at 

 right angles to their axis the former, those cut at an angle of 

 45 to their axis. It is thus seen that the long axis of a mus- 

 cular fibre corresponds, in relation to its properties of double 

 refraction, to the axis of crystallization of a uniaxial crystal 

 in short, that a muscular fibre is optically comparable to such 

 a crystal. Briicke has further demonstrated, not only that the 

 muscular fibres are uniaxial, but also that they are positive, 

 i. e., that they resemble those uniaxial crystalline bodies in 

 which the extraordinary index of refraction exceeds the ordi- 

 nary index. Inasmuch as the apparatus necessary for demon- 

 strating this is not to be found in most laboratories, and an 

 explanation of the mode in which it is accomplished would in- 

 volve a more general discussion of the subject of polarization 

 than our space allows, it has been omitted. The reader is re- 

 ferred to Briicke's article in Strieker's Histology for further 

 information. 



If a teased preparation of the fresh muscle of a frog is 

 treated with water and covered, the ends of the muscles swell, 

 and the contents project as a transparent granular mass, in 

 which the strife are no longer visible. Between crossed Nicols 

 these parts are found to be doubly refractive, and look like a 

 silver-gray cloud of dust on the dark ground. The particles 

 of which the cloud consists are regarded by Briicke as the 

 real elements of the doubly refracting substance. They are 

 the constituents of the sarcous elements, and are called Dis- 

 diaklasts. The disaggregation of the sarcous elements is de- 

 termined by the water. 



