TISSUES OF SPECIAL FUNCTION. 85 



of an object under observation. It is rarely that sections happen 

 to be made in such a direction that they reveal the complete struct- 

 ure of an object. It is nearly always necessary to study the appear- 

 ances presented by the section, and to infer what the structure of 

 the object must be in order to yield the appearances seen. This is 

 sometimes a matter of considerable difficulty. 



If the plane of the section lie parallel with the long axes of 

 the cells, the nuclei of the latter will appear as rod-like or long, 

 oval bodies lying parallel to each other and distributed at regular 

 intervals throughout the tissue. The outlines of the cells will be 

 distinctly visible in some places, but in most of the section the 

 boundaries of the deeper cells will be obscured by the bodies of 

 the cells at the surface of the section, and the borders of the latter 

 will be difficult of detection, because in many places the knife has 

 left only a portion of the cell with a very thin and transparent 

 edge (Figs. 69 and 70). For the practical recognition of the tissue, 

 when cut in this direction, we must, therefore, in many cases, 

 depend solely upon the shape and distribution of the nuclei and 

 the color of the material between them after the section has been 

 treated with certain stains (e. g., eosin). 



If the cells of the tissue have been cut perpendicular to their 

 loner axes, the section will contain true cross-sections of the indi- 



o 



vidual fibres. These appear as round, oval, or, more usually, 

 polygonal areas of various size, according to the part of the cell 

 included in the section. If the cell has been cut near one of its 

 ends, the cross-section will be small ; if near the middle, it will be 

 large, and will contain a cross-section of the nucleus, situated near 

 its centre and appearing as a round dot (Fig. 71). It is in 

 such sections that one may sometimes see the minute prickles 

 or ridges, already referred to, projecting from the cell-bodies 

 and joining with those of the contiguous cells to form delicate 

 bridges across the narrow intercellular spaces. The only tissue 

 with which this aspect of smooth muscular tissue is liable to be 

 confounded is dense fibrous tissue, as seen in the cross-sections of 

 tendons or ligaments (Fig. 66). There we also see polygonal areas 

 of various sizes, separated for the most part by only a thin layer of 

 cement. But these areas never contain nuclei, because they are 

 composed, not of cell-bodies, but of intercellular substance. The 

 nuclei of the flattened connective-tissue cells may be seen here and 

 there apparently lying within the cement, the body of the cell being 



