78 EPITHELIAL TEXTURES HAEDBXED 



tliose near the growiBg part it can always be readily 

 demonstrated by the aid ©f the carmine fluid, § 68. 

 The structure and mode of growth of these tissues 

 are well illustrated in the long, ragged, hair-like 

 process found upon the summits of the filiform papillae 

 in the central part of the dorsum of the human 

 tongue, for the individual cells can be distinguished in 

 almost every part of the hair- like process ; and as 

 they are not closely matted together, as in the hair, 

 nail, and liorn, their arrangement can be very satis- 

 factorily demonstrated. These hair-like processes can 

 be obtained by slightly scraping the dorsum of the 

 tongue with a knife. The bioplasm can be seen, not 

 only in the young growing cells at the base, but in 

 those that are mature in the lower part of the shaft, 

 and with a little management the constituent cells 

 can be isolated from one another and examined sepa- 

 rately. In many of my specimens the bioplasm is 

 beautifully distinct and well coloured by the carmine 

 fluid, while numerous new centres (nucleoli) can be 

 discerned which are more intensely coloured than the 

 rest of the bioplasm. The formed material is per- 

 fectly destitute of any coloiir whatever. By examining 

 structures of this kind, the student will be able to 

 form an opinion concerning the great advantages to 

 be derived from practising the staining process. 



H9. Epithelial textures hardened with ralcareoiis 

 matter. — I will now advert to the remarkable changes 

 which occur during the formation of those very hard 

 tissues which are infiltrated with calcareous salts, and 

 in which the bioplasm plays a conspicuous part. In 

 illustration, I will di'aw attention to the formation of 

 two of the hardest and most durable textures in the 

 body — the enamel and dentine of the tooth. Although, 

 in their fully developed state, these tissues are remark- 

 able for the large proportion of earthy salts they con- 

 tain, there was a time when each was composed of 

 very soft organic matter only. Although no trace of 



