CHAP. VII.] STEIPED MUSCLE. 153 



side of the dark points seen on the separated fibrillae ; but some 

 believe these stripes to be present only on the surface of the fibre, 

 and to be formed by the spiral windings of a filament. Consider- 

 able diversity of opinion also exists as to the nature of the alternate 

 light and dark points seen on the individual fibrillse ; some con- 

 ceiving them to indicate a single spiral, others a double spiral 

 arrangement ; some imagining them to be minute zigzag bendings, 

 others indentations, and others still that they depend on the alter- 

 nation of two kinds of substance. On this account we shall explain 

 in a few words our reasons for adopting the view above sum- 

 marily given. A soft mass made up of an immense congeries 

 of highly refracting particles cannot but exhibit many deceptive 

 appearances when viewed by transmitted light, and through glasses 

 of bad defining power. The slightest disturbance of its interior 

 structure will affect the refractions, which will thus be readily 

 made to disguise and modify the true form and arrangement of its 

 integrant parts ; on which account .great care and circumspection, 

 and a total freedom from bias, are requisite for an observer who 

 would not be misled to mistake appearances for realities. 



That the stripes are not caused by a structure distinct from the 

 fibrilla?, and present only on the surface of the fibre, is evident from 

 the following facts : 



1. That a transverse section of a fibre 

 shews it to be solid, and not hollow ; 

 and that the ends of fibrillse, as seen 

 on the section, exist throughout its 

 interior just as on its surface (fig. 38). 



2. That fibrillae taken from any part 

 of a fibre are marked with light and 

 dark points, corresponding in distance 



nrirl fnrpp with flip trjin<ivpr!P <sfrinp<s rvf Transverse section of three elementary 



e witn tne transverse stripe^ 01 fibres of the dried pectoral musc]e of . th * 



flip fihrp Teal (Querquedula crecca), treated with 



weak citric acid; showing the round re- 



3. That with a high magnifying 

 power, applied to a thick fibre, we may ^%*Z&%% the 

 bring all parts of its interior into focus 

 in succession, and perceive throughout the same kind of stripes. 



The occasional appearance, therefore, of these stripes being con- 

 fined to the surface is deceptive. They are sometimes more strongly 

 marked there, partly because there is a greater condensation of the 

 tissue there, and partly from the circumstance of the fibre being 

 usually immersed, when examined, in a fluid of less density than 

 itself. This appearance is always greatly diminished by placing 



