414 



The author then proceeds to describe the involuntary muscular 

 tissue as it presents itself in two situations where he has recently 

 examined it, namely, the minute arteries of the frog's foot and the 

 small intestine of the pig. He finds that, by suitable manipula- 

 tion, exceedingly delicate arteries may be dissected out from the 

 web of the frog, some of them being of smaller calibre than average 

 capillaries; and that in such vessels the middle coat consists of 

 neither more nor less than a single layer of Kolliker's muscular 

 fibre-cells wrapped spirally round the internal membrane, and of 

 sufficient length to encircle it from about one and a half to two and 

 a half times. The tubular form of the vessels enables the observer, 

 by proper adjustment of the focus, to see the fibre-cells in section ; 

 and where the nucleus is so placed in the artery as to appear in 

 section also, the section of the nucleus is invariably found surrounded 

 on all sides by that of the fibre-cell, whence it is inferred that the 

 nucleus is not merely connected with the external part of the mus- 

 cular element, but is embedded in its substance. Considering that 

 no tearing of the tissue is practised in the preparation of the objects, 

 but that the parts are seen undisturbed in their natural relations, 

 this simple observation appears to prove conclusively, that, in the 

 arteries of the frog''s foot, the involuntary muscular tissue is con- 

 stituted as KoUiker has described it. 



The pig's intestine proved to be a very favourable situation for 

 the investigation of unstriped muscle, the fibre-cells being larger 

 than in the human subject in the same situation, and very readily 

 isolated by simply teasing out a small portion of the tissue with 

 needles in a drop of water. Under these circumstances, they 

 corresponded exactly with Kolliker's descriptions, and the deli- 

 cate and perfect form of their tapering extremities was sometimes 

 seen to be such as could not possibly have been produced by the 

 tearing of a continuous fibre. In one fibre-cell that happened to be 

 coiled up, the position of the nucleus embedded in its substance was 

 seen in the same way as in the arteries of the frog. In examining 

 the circular coat of a contracted piece of intestine from a freshly 

 killed pig, the author observed some short, substantial-looking bodies 

 of high refractive power, each of a somewhat oval shape, with more 

 or less pointed extremities, and presenting several strongly-marked, 

 thick, transverse ridges upon its surface ; and each, without excep- 



