ENGELMANN ON CONTRACTILITY AND DOUBLE REFRACTION. 41 



After the interposition of a gypsum plate, i.e. with parallel 

 Nichol's prisms, the rays that lay diagonally appeared of a 

 pale blue and yellow colour respectively on a dark reddish- 

 violet ground. 



The double refraction of the rays was positive with respect 

 to their long axes. 



Each protoplasmic ray behaved like a positive double- 

 refracting uniaxial fibre whose optic axis lay parallel to the 

 long axis of the fibre, and in general parallel to the direction 

 of shortening. 



5. First appearance of Douhle Refraction and Contractility 

 duriyig the development of Striped Muscles-fibres . — Valen- 

 tin's researches on this point seemed to justify the following 

 conclusions : 



First. That the heart muscle of the chick shows no trace 

 of double refraction several days after the appearance of 

 contractility. 



Second. That the double refraction of striped muscle is 

 visible before the appearance of striation. 



Engelmann, from numerous observations, denies the truth 

 of the first conclusion. 



For in the course of the second day of incubation he finds 

 that the heart muscle is distinctly though feebly double 

 refracting, and is positive in reference to the direction of 

 shortening when the most highly developed muscles were 

 about '02 to "03 mm. in thickness, and about twice or three 

 times as long as this. 



They consisted of spindle-shaped cells, each possessing an 

 ellipsoidal nucleus and a nucleolus. In the perfectly fresh 

 condition neither nucleus nor cell-boundaries were visible. 



The muscle-bundles seemed to consist of a homogeneous 

 protoplasm possessed of a tolerably high refractive power. 

 In this protoplasm lay scattered here and there small highly 

 refractive granules. No trace of striation was noticed either 

 in the fresh state or after treatment with alcohol (30 — 60 

 per cent.), Miiller's fluid, or perosmic acid (^ — 1| per cent.) 

 Polarised light was used as well as ordinary light, but 

 the results were negative. 



Striation appeared in the heart muscle from the third to 

 the fourth day of incubation, but already the double refract- 

 ing capacity was highly developed. Probably the origin of 

 striation in the heart muscle depends on the fact that double 

 refracting particles already present, but distributed uniformly 

 in an isotropous ground substance, arrange themselves 

 regularly in groups, viz. strisc, between which are left layers 

 of a clear singly refracting substance. 



