106 GLANDS. 



pass beyond its limits; as their growth in length, 

 however, goes on, they curve and twist upon them- 

 selves, so as to form the glomeruli which we find in the 

 adult. Whilst these changes are taking place in the 

 size and external shape of the sweat glands, their inte- 

 rior is observed to become converted into a canal, and 

 this is probably effected by the disaggregation and 

 melting down of the central cells. Finally, the walls 

 of the gland tubes are perfected by a series of morpho- 

 logical transformations of the more superficial cells of 

 the original cylinder. 



Preparations. The specimens required for the study of the tubu- 

 lar glands are very readily prepared. It is simply 

 necessary to detach, by means of scissors, very deli- 

 cate little lamellae from the mucous membrane of the 

 intestine, cutting both parallel with, and at right 

 angles to, its surface. For those of the skin, a razor 

 is employed in the same manner, and dilute solutions 

 of potassa and acetic acid are applied to the speci- 

 mens in order to render the tissues more trans- 

 parent.* 



Kidneys, struc- Kidneys. In a longitudinal section of a kidney, 

 including its Tiilus, the parenchyma of the gland pre- 

 sents itself in two obviously different aspects ; near 

 the liilus, and towards the centre of the gland, it is 

 striated ; elsewhere it is granular in appearance. The 

 striated portion (cones, medullary substance, pyramids 

 of Malpighi) consists of sections of cones, of which the 



* The spiral twist of the duct of the sweat gland, as it traverses the 

 epidermis, is best seen by cutting thin slices from the edge of a piece 

 of dried skin of the palm of the hand or sole of the foot, with a sharp 

 scalpel. (Ed.} 



tare. 



