On the Relations of the isotropous to the anîsotropous Layers in striped Muscles. 535 



able forms but also their regular changes during contraction to be 

 accounted for. The appearance may be due to the form , but the 

 form must be due to some constitutional heterogeneity of which it is 

 to be considered as the expression. 



3) At the commencement of contraction, the isotropous layer dis- 

 appears, while measurements show that the anisotropous or stained 

 layer lengthens (cf. diagram Fig. 24). This may perhaps mean that 

 the isotropous substance has mixed with the anisotropous, causing 

 its slight increase in length. This is the German "Uebergangsstadium", 

 when, under ordinary light, all striation except Krause's discs dis- 

 appears (Figs. 15, 16, 17, and part of 14). Under polarised light, 

 however, the striation is still visible, and Engelmann assumes there- 

 from that the isotropous layer persists per se 0, and that the slight shor- 

 tening of the element is due to the active contraction of the anisotropous 

 layer. I think, however, taking into account the diffusion of the stain 

 which was formerly confined to the anisotropous layer, that the above 

 is the more probable explanation viz : the anisotropous substance has 

 drawn in the isotropous, at the same time consequently itself increasing 

 in length. The apparent persistence of the isotropous layers in polarised 

 light may be explained as due to an optical change produced in the ends 

 of the anisotropous layers by mixture with the isotropous. On the 

 other hand , it is of interest for our point that Engelmann has to 

 assume that the isotropous layer gives up something (i. e. „water") to 

 the anisotropous. Merkel^) has further tried to explain the pheno- 

 menon as a mixture of the "plasmatic" (isotropous) substance 

 with the "disdiaklastic" which, compounded with a "kinetic" substance, 

 forms the anisotropous layer. Schäfer also describes the isotropous 

 substance as retreating into the anisotropous, which, in wing muscles 

 of Flies has, as shown by his photographs, a regular structure for its 

 reception. Again, Krause ^) describes the isotropous layer as drawn 

 in between a number of stiff longitudinally arranged rods composing 

 the anisotropous layer. There is thus considerable evidence in favour 

 of the view that the molecules of isotropous substance are drawn in 

 in some way among the molecules of anisotropous substance. This 

 might take place: 



1) Neue Untersuchungen uber die mikrosk. Vorgänge bei der Muskel- 

 contraction, in: Pflüger's Archiv, Bd. 18, 1878. 



2) Ueber die Contractionen der quergestreiften Muskelfaser, in; 

 Arch. f. mikr. Anatomie, Bd. 9, 1881. 



3) Handbuch der allgem. und mikr. Anatomie, 1876, p. 22. 



