40 



THE ESSENTIALS OF HISTOLOGY. 



their distinct outline, their straight course, the fact that they never run 

 in bundles, but singly, and that they branch and join neighbouring 

 fibres. If broken by the needles in making the preparation, the elastic 

 recoil causes them to curl up, especially near the broken ends. Besides 

 the microscopical differences, the two kinds of fibres differ also in their 

 chemical characters. Thus the white fibres are dissolved by boiling in 

 water, and yield gelatin ; whereas the substance of which the elastic 

 fibres are composed (elastin) resists for a long time the action of boiling 

 water. Moreover, the white fibres swell and become indistinct under 

 the action of acetic acid; the elastic fibres are unaltered by this reagent. 

 The bundles of white fibres which have been swollen out by acid 

 sometimes exhibit curious constrictions (fig. 40). These are due either 

 to elastic fibres coiling round the white bundles, or to cell-processes 

 encircling them, or to an investment or sheath which remains un- 

 broken at certain parts, and thus prevents the swelling up of the 

 bundle at these places. 



FIG. 42. SUBCUTANEOUS TISSUE FROM A YOUNG RABBIT, PREPARED AS DIRECTED 

 IN 1. (Highly magnified.) 



The white fibres are in wavy bundles ; the elastic fibres form an open network, p, p, plasma- 

 cells ; g, granule-cell ; c, c', lamellar-cells ; /, fibrillated-cell. 



The cells of areolar tissue. Several varieties of connective-tissue 

 cells are distinguished, viz. : (1) Flattened lamellar-cells, which are often 

 branched (fig. 42, c, c'), and may be united one to the other by their 

 branches, as in the cornea, or are unbranched and joined edge to edge 



