THE CONNECTIVE TISSUES 



31 



ground- substance between the bundles can with difficulty be seen in 

 the fresh tissue on account of its extreme transparency ; but it can be 

 brought to view by staining with nitrate of silver, as in 4. The whole 

 of the tissue is thereby stained of a brown colour, with the exception of 

 the spaces which are occupied by the corpuscles (cell-spaces, fig. 31). 



Besides the white fibres of connective tissue here described, fibres 

 of a different kind (fig. 32) may be made out in the preparations ; 



FIG. 32. 



A. Elastic fibres of areolar tissue. From the subcutaneous tissue 

 of the rabbit. B (from Toldt). A white bundle swollen by acetic 

 acid. From the subarachnoid tissue at the base of the brain. 



these are the elastic fibres. They are especially 

 well seen after treatment with acetic acid, and 

 after staining with magenta ; but they can be de- 

 tected also in the fresh preparation. They are 

 characterised by 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 boil- 

 ing 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. 32). These are due either 



