8o PRACTICAL HISTOLOGY. 



rings of cat, hardened in per cent chromic acid ( 6). 

 The specimen will be a valuable one if the section be made 

 with the freezing microtome ; for in that case the ciliated 

 epithelium lining the trachea will not be destroyed, as is 

 apt to be the case when such a tissue is imbedded in 

 paraffin. Mount the section in Farrants' solution or in 

 glycerine, and examine. 



(L.) The position of the cartilage, epithelium, and the 

 tracheal glands. 



(H.) a. The cartilage, consisting of cells in a hyaline 

 matrix. Observe the nucleus and granular protoplasm of 

 which the cells consist ; the distribution of the cells in the 

 matrix; the groups result from recent proliferation of the 

 cells. 



b. The periehondrium, consisting of white fibrous tissue. 

 Notice the gradual transition between the matrix of the 

 cartilage and the fibres of the periehondrium on the one 

 hand, and between the cells of the cartilage and those of 

 the periehondrium on the other. The latter, however, are 

 difficult to discern unless they are stained. 



c. The ciliated epithelium. The characters of the ciliated 

 cell have been already studied. The cells are here seen in 

 situ. There are several layers of them, but only the upper 

 layer (those next the cavity of the trachea) are ciliated. 

 The others are of irregular shape, and are apparently young 

 cells that are destined to develop into those with cilia. 



d. The glands, cut in all directions, will be found inside 

 the cartilage. They are lined by epithelium, and their 

 ducts may perhaps be traced to the inner aspect of the 

 membrane on which they pour their mucous secretion. 



1 1 6. Costal Cartilage of human adult kept for 

 twenty-four or forty-eight hours in a saturated solution of 

 picric acid. With a razor make a thin T. S. through a 

 point of incipient ossification. Mount in Farrants' solution 

 or in glycerine, and examine. 



(H.) The diffuse yellow colour resulting from the picric 

 acid might be removed by immersion in water or in alcohol, 

 but it is advantageous to retain the colour in this case. 

 At the point of incipient ossification groups of proliferating 



