120 PRACTICAL HISTOLOGY. 



c. Osmic acid is also a good hardening agent. Small portions of 

 the glands are hardened for two days in \ per cent solution. They 

 may then be cut by freezing, or may be farther hardened in alcohol and 

 cut by the hand. This method of hardening is especially suitable when 

 it is desired to dissociate the gland elements with needles. The sec- 

 tions are mounted in Farrants' solution, or in potassium acetate solu- 

 tion. 



206. Structure. The salivary glands and pancreas 

 have an essentially similar structure. They are all racemose 

 glands ; the ducts lined by columnar epithelium, and the 

 acini containing polyhedral epithelial cells, with channels 

 for the secreted fluid occurring here and there between, 

 them. The secreting cells of the submaxillary gland differ 

 from those of the parotid and pancreas in containing 

 mucin. 



Examine (L.) a section of submaxillary gland, prepared 

 stated in 205, a. The acini. 



(H.) The cells of the acini and those of the ducts. 



KIDNEY. 



207. Methods. (a.) The epithelium of the fresh 

 kidney may be examined by merely scraping the surface of 

 a Malpighian pyramid cut vertically, and examining the 

 scraping in salt solution. 



b. Sections of the fresh kidney may be made with a 

 Valentin's knife (Fig. 56), but far better with the freezing 

 microtome. Sections of the unhardened kidney can scarcely 

 be preserved. 



c. The best ordinary methods for preparing the kidney 

 are precisely the same as in the case of the liver. There- 

 fore all that is stated in 199. a applies equally to both. 



d. Small pieces of kidney may also be hardened in a 

 solution of chromic acid. The kidney of the rabbit may 

 be very successfully hardened in i per cent solution, as 

 directed in 9. 



e. The renal tubules may be isolated (Ludwig) by making thin 

 vertical sections of the Malpighian pyramids of the fresh kidney, and 

 putting them in a flask containing one part of hydrochloric acid to four 

 parts of rectified spirit. A cork, with a long glass tube passing through 

 it, is fitted to the flask, and it is boiled over a sandbath for two or three 



