STRIATED MUSCULAR FIBRE IN MAMMALIA. 
255 
decidedly oval, generally measuring in their long axis somewhat more than 
(iTooth), and in their short axis ^^th. Their outline becomes broader and paler, 
and is less distinctly defined ; their contents grow more plainly granular, and between 
their margin and contents, that is immediately within their softened outline, a clear 
bright ring may be observed. 
Their characters may in some respects be more easily investigated, and the changes 
they undergo can be more obviously traced as they lie imbedded in the substance of 
muscular fibre. The walls of the nuclei are firm and far more resisting than the 
substance of the fibre ; for when the fibre is stretched and narrowed between them, 
the nuclei remain unaltered in shape and bulge the fibre at the part where they are 
situated ; and it may be constantly observed that when young fibres float freely in 
liquid they never bend at the points where the nuclei are situated, but always at some 
part between them. A sudden bend or twist is often seen just beyond the extremity 
of a nucleus, but the nucleus itself preserves its shape, and renders that portion of 
the fibre which it occupies comparatively firm. 
As the nuclei lie in the substance of the fibre they increase considerably in size, 
and become fainter in appearance. The change in their shape and outline, and the 
bright border immediately within their circumference, are generally distinctly traced; 
they seem at last to be filled with granules, and as these are more plainly developed 
their walls become broken and obscure, until at last their position is marked by an 
irregular cluster of granules, which remain very visible for a short time and then 
rather suddenly disappear. 
These granules have many of the characters of minute oil-globules ; they appear 
either as dark or as bright highly refracting spots, with a thick, dark and well- 
defined border, according to the focus at which they are viewed. When the tissue 
is preserved in spirit for some time, many of them fuse together into larger globules, 
which in aspect and other characters completely resemble globules of oil. They are 
not readily acted on by ether, but the granules disappear in fibres that have been 
preserved for a short time in it. Except at the latter periods of development, 
the nuclei can be readily discerned in the substance of the foetal fibres without any 
previous preparation, unless the structure of the fibre is obscured by the deposit of 
fresh and undeveloped material upon its surface. Towards the close of foetal life, as 
the tissue grows more dense, the nuclei are discerned with greater difficulty ; they 
become obscured by the substance of the fibre; in either case, if the tissue be pre- 
served for a day or two, or if placed for a short time in water, the muscular sub- 
stance is rendered much clearer and the nuclei become distinctly visible. The same 
plan of simple maceration in water succeeds so well, even with muscular fibres at a 
far more advanced period of development, that the nuclei they contain may be thus 
beautifully shown. In a day or two the substance of the fibre becomes clear and 
transparent and the nuclei appear ; the advantage of this simple plan is, that the 
nuclei remain unaltered ; they preserve their natural appearance. The addition of 
