242 MUSCULAR FIBEES IN POLARISED LIGHT, BY E. BRUCKE. 



field. Here the sarcous elements have become disturbed, whilst 

 the absorbed water has shifted the several disdiaclasts from 

 their position. This state, resulting from the imbibition of 

 water, is essentially different from that induced by the action 

 of dilute acids, which effect a change in the substance of the 

 disdiaclasts themselves, and take away their power of doubly 

 refracting light. In conclusion, I will add a few remarks on 

 the external and internal aids to the study of muscular fibres 

 in polarised light. 



To whomsoever the foregoing details and the ordinary works 

 on physical science are insufficient, Aug. Beer's Introduction to 

 the Higher Optics* will prove of service. In the choice of an 

 instrument it is in the next place to be noted that the upper 

 Nicol's prism should be placed over the ocular, and not between 

 the objective (in the more restricted sense of the word) and the 

 so-called collective. Amongst instruments constructed with 

 the latter arrangement I have found nothing better adapted 

 than this for minute and difficult investigation. Bottger, of 

 Berlin, originally furnished the best Nicol's prisms for these 

 purposes; more recently, however, Hartnack, in Paris, has 

 constructed an admirably perfect instrument, arranged accord- 

 ing to a method described by him and Prazmowski in the 

 " Annales de Chemie et de Physique," 4 e se'rie, T. vii. 



The microscopic image can be rendered still more beautiful 

 by distributing the muscular fibres upon a plate of gypsum or 

 mica, attached to the stage by means of Canada balsam, Dam- 

 mar resin, or Jeffrey's solution of mastic and caoutchouc in 

 chloroform. By appropriate inclination of the gypsum or mica 

 plate a coloured field is obtained, from which the muscles are 

 projected, tinted with different colours, varying in proportion as 

 their inclination on the plate increases or diminishes the differ- 

 ence of the paths which the rays respectively pursue. This 

 experiment has the additional advantage, that the isotropal 

 portions do not entirely vanish as in the dark field, but remain 

 apparent, tinted with the colour of the ground. The most 

 beautiful effects are obtained when the thickness of the little 

 plate is so proportioned that when the prisms are parallel to 



* Brunswick, 1853, 800. 



