BEHAVIOUR OF MUSCULAR FIBRES IN POLARISED LIGHT. 241 



discoverer of double refraction in calc spar, in the title to his 

 well-known treatise.* The composite nature of the sarcous 

 elements furnishes an explanation of the various appearances 

 presented by muscles in a state of rigor mortis. In my re- 

 searches on the structure of muscular fibres with polarised 

 light,f I have constructed nine different schemes, and we may 

 not unfrequently see one and the same muscular fibre in dif- 

 ferent parts representing two different schemata, which is at- 

 tributable to the circumstance that, in the several sections of the 

 fibre, the sarcous elements have divided with great regularity 

 into smaller groups of disdiaclasts, so that much narrower 

 systems of transverse strise appear in these sections than in 

 others, though they are neither shortened nor thickened by 

 contraction. 



MargoJ who found that the sarcous elements exist also in the 

 fibres of the adductor muscle of bivalves, frequently saw the 

 muscles in Anodonta only partially striated. In this case the 

 sarcous elements of the transversely striated parts lie next one 

 another in regular rows ; but in those parts that, with weak 

 powers, appeared homogeneous, he found, with higher powers, 

 instead of numerous small irregularly distributed granules, small 

 groups of disdiaclasts. 



If the living muscular fibres of frogs or beetles be immersed 

 in water, they, as is well known, die rapidly ; the ends swell 

 up strongly, and the contractile contents ooze out of the 

 sareolemma. If such terminal portions of fibres be observed 

 under the polarising microscope, with the prisms crossed, no 

 sarcous elements are observed in them, but they present the 

 appearance of fine silvery-grey clouds distributed in the dark 



* JExperimenta Crystalli Islandici Disdiaclastia quibus mira et insoliia 

 Refractio detegitur. Havn, 1869. 



t Denkschriften der Wiener Akademie der Wissenschaften, Band xv. r 

 Separataujlage Wien. bei Gerold. 



\ Uber der Muskelfasern der Mollusken, Sitzungsberichte der Wiener 

 Akademie, Band xxxix., s. 566. 



The fibres of the adductor muscle were originally erroneously regarded 

 as smooth muscular fibres ; that is to say, the substance of which is doubly 

 refracting, but in which neither sarcous elements nor isotropal intervening 

 substance can be distinguished. 



