56 HORNY TISSUE, 



the same manner as upon the epidermis, converting it into a mass 

 of colourless non-nucleated vesicles ; but, according to Kdlliker, a 

 dilute solution of caustic soda brings into view the most beautiful 

 polygonal or oval cells, with distinct nuclei. 



The fibrous structure of cows' horn disappears under the pro- 

 longed action of a concentrated solution of potash, but no cells 

 (especially nucleated ones) become distinctly visible until water 

 has been poured over the object. After repeated neutralisa- 

 tion with sulphuric, or even acetic acid, the cells generally appear 

 in the form of oval or spherical vesicles without contents ; the 

 nuclei have consequently disappeared. 



Whalebone consists, according to Mulder and Donders, who 

 have subjected it to a very exact histo-chemical examination, of 

 thin lamellae, which lie parallel to the outer surface, and to the 

 tubular system which resembles the medullary canals. Each of 

 the lamellae consists of a number of compressed cells, which are 

 brought into view by the action of water after they have been treated 

 with concentrated caustic potash. In this case, also, the cell-wall 

 resists the action of the reagents for a much longer period than 

 the nucleus and the other contents. 



The same observers were also the first who accurately examined 

 tortoise-shell ; they found that this tissue also breaks up into 

 polygonal and oval cells on the application of caustic alkalies, 

 although a much more prolonged action of the potash is neces- 

 sary here than in the case of the above-described horny tissues. 

 The cells are not very readily isolated, and it is only on the addi- 

 tion of water that they appear individually ; they are without 

 nuclei, but always contain a slight amount of granular substance. 

 Moreover, independently of the cells, granular matter is always 

 perceptible on the addition of water. 



Acetic acid, even when concentrated, scarcely produces any 

 action on epidermis, even after it has been softened by water ; but 

 by prolonged boiling with concentrated acetic acid, the scales 

 become isolated, and swell into extremely pale, distended, but still 

 somewhat flattened vesicles, entirely devoid of granules or nuclei. 

 According to Kolliker, the walls of the epidermic cells do not dis- 

 solve, but only those of the cells of the rete mucosum. 



Acetic acid acts upon the substance of the nails in thesame manner 

 as upon the epidermis, only with less rapidity; it generally causes the 

 nuclei of the cells to come beautifully and prominently into view. 



Cows 3 horn is very little affected by the action of concentrated 

 acetic acid, even after prolonged boiling ; and the microscope 



