416 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 



is the chief cause of the formation of giant-cells ; which are, 

 nioreover^ found in large numbers on the external surface of 

 masses of callus, where there is no appreciable pressure. Still 

 it was possible to produce atrophy with giaut-cells artificially 

 in animals, by long-continued local pressure on a bone; but 

 they were also found in the interior of the bone, where 

 pressure could not of course operate directly. Further, the 

 author found that giant-cells wei-e developed in the lymph- 

 sacs of frogs, after the irritation caused by the introduction of 

 various foreign bodies, so that he considers their formation to 

 be largely due to an alteration of nutrition, wliich is perhaps 

 brought about by pressure. Amoeboid movements were seen 

 in some giant-cells, but not in others, especially in those 

 whose protoplasm contained fatty granules. The author 

 therefore draws a distinction between "fixed" and "migratory" 

 giant-cells. In the latter, division was seen. The author 

 concludes that giant-cells may be developed from any form of 

 cell, and that their appearance in bone is not secondary to the 

 formation of Howship's lacunae. 



VI. Muscle. — 1. Structure and Action of Striated Muscular 

 Fibre. — Dwight (' Proc. Boston Soc. Nat. Hist.,' vol. xvi, 

 Nov., 1873) used the legs of Gyrinus, which are sufficiently 

 transparent to permit the examination of their muscles in 

 sitil: When at rest, but extended between its points of 

 attachment, the fibre is straight-bordered, and shows a series 

 of broad grey bands with a white border, separated by narrow 

 black granular bands. When the fibre is free from all strain 

 or resistance (as when one of its attachments is divided or 

 moved much nearer to the other), the fibre is much broader, 

 the black bands a little narrower and closer together. The 

 white and grey stripes are also narrower, especially the 

 former. The fibre has a scalloped border, the greatest 

 bulging being opposite the middle of the grey. When the 

 fibre is stretched it is narrower, with a more sharply defined 

 outline. The black granular bands become separated into 

 two parallel dotted lines, separated by a clear space. The 

 grey bands become lighter and the white borders darker, so 

 that the distinction between the two is less clearly marked. 

 The state of active contraction is difficult to observe, owing 

 to the incessant changes as the wave passes along the fibre. 

 A part of the fibre is seen to dilate, the black bands become 

 more prominent, approach each other, and seem to run with 

 the wave along the fibre. The grey bands (the contractile 

 element) disappear, so that there is only an alternation of 

 black and white stripes, the borders of the fibre being very 

 frequently, probably always, festooned or scalloped. The 



