HORNY TISSUE. 53 



dermic and epithelial cells, and the cells of the glandular follicles 

 (Kolliker), are composed of a protein-body, that is to say, a sub- 

 stance far more nearly allied to albumen and fibrin than to the 

 matrix of elastic tissue, seeing that they are readily soluble in acetic 

 acid, and in very dilute alkalies. 



HORNY TISSUE. 



IN former times the tissues belonging to this class were regarded 

 as amongst the simplest in the animal organism, and considered 

 merely as different forms of one and the same matrix, which cer- 

 tain chemists were ready enough to discover, and to designate by 

 the term Keratin. The zealous labours of recent histologists have, 

 however, shown us that even these apparently homogeneous tissues 

 have a complicated, and in many respects, a variable structure. 

 There exists the same correspondence between the structure of 

 the epidermis, the nails (claws and hoofs), the horns, and whale- 

 bone, as that which we observe in the chemical constitution of 

 these tissues, all of which are so far analogous to one another that 

 they proceed from cells or nucleated vesicles, which are not morpho- 

 logically developed like the cells of other organs, but to a certain 

 extent dry up, and are only agglutinated together by an inter- 

 cellular substance, which often does not very readily admit of 

 detection. They also exhibit great resemblance in a chemical 

 point of view, for when compared with other tissues they all 

 contain a large quantity of sulphur in combination with a sub- 

 stance, or with atomic groups, whose origin from, or affinity with 

 the so-called protein-bodies cannot be denied when we consider 

 their behaviour towards certain reagents, and their per-centage com- 

 position. Although we are still far removed from a correct know- 

 ledge of the chemical constitution of these tissues, or rather of 

 their elements, chemistry has, nevertheless, very largely contributed 

 to place the question of the histological conformation of these 

 tissues on a level with the present state of science; in confirmation 

 of which we need only indicate the admirable labours of Donders* 

 and Mulder, of Paulsent, KollikerJ and several other observers. 



* Hollandische Beitrage. Bd. I, S. 39 u. 126, and Mulder's Vers. ein. 

 physiol. Chem. S. 542-579 [or English Translation, pp. 493-530]. 



t Observationes inikrochemicse ; diss. inaug. Dorpati Liv. 1848. 

 t Mikrosk. Anat. Bd. 2, S. 58-62, u. 85-88. 



