80 HISTOLOGY OF THE POISON-GLANDS OF BUFO AGUA. 



While the literature on these skin glands of various batrachians is fairly extensive, 

 Bristol and Bartelmez are apparently the only authors who have dealt with the toad at 

 present under consideration. In a short note in "Science," they say: 



"The poison glands are found only on the upper surface of the body, while the mucous glands 

 are found all over the skin and are crowded together in large parotid 'glands' behind each ear. 

 They are much larger than the mucous glands and extend deep down into the compact corium layers. 

 They are surrounded by a thin layer of loose connective tissue, which contains nerve fibers and a 

 dense network of capillaries. There is an almost continuous layer of smooth muscle fibers about 

 the gland. The cells of the glandular epithelium develop to an enormous size, and when mature 

 they disintegrate, their entire plasm becoming the secretion, so that when a poison gland has reached 

 its lull development it is simply a reservoir of poison. When the poison is discharged the remains 

 of the gland are resorbed and at the same time one of the five or six undeveloped glands, grouped 

 around the mouth of the functioning gland, grows down alongside the remains of the discharged 

 gland, pushing it aside to occupy its former place." 



THE GLANDS. 



The parenchyma of the parotid and other skin glands is buried deep in the cutis vera 

 (figs. 2, 3, 5, and 7), so that if the skin in the parotid region is stripped off the gland comes 

 away in the skin flap. When such a cutaneo-glandular flap is everted the tremendously 

 rich nerve and blood supply to the gland is very striking. Huge arteries and veins come to 

 and leave the gland-bearing region from the brachial vessels, accompanied in their course 

 by nerves which supply the gland. 



The under surface of the skin flap is silvery white in color and is thrown into deep 

 hollows and ridges by the huge batteries of the gland above. In the region beneath the 

 gland, numbers of corial melanophores fleck the silver background with a tiny irregular 

 gray-black mottling. 



If these glands are cut through with a razor a matter somewhat difficult of accom- 

 plishment, since the skin of the animal is extremely tough and the glands discharge very 

 readily on the lightest pressure after removal from the body if these glands are cut 

 through without emptying the batteries, the latter may be seen outlined against the sur- 

 rounding connective tissue of the corium as dark yellowish gray sacks, not unlike a Chianti 

 flask in shape, the flask's neck being represented by the ducts of the gland. 



We have spoken of the toughness of the skin of the toad, and not without reason. So 

 tough it is that the preparation of frozen sections from it, without loss of the glandular 

 secretion, is impossible, and even by the use of the celloidin or paraffin methods of embed- 

 ding the retention of the glandular content intact in thin sections is a matter of great 

 difficulty. We have found the celloidin technique the most satisfactory for our purpose. 



The poison-gland can be, as Muhse stated, divided into neck, collar, and acinus, and is, 

 developmentally, a part or downgrowth of the epidermis. 



Each mature adult gland of these toads can be seen in section to have its duct encircled 

 by a ring of young glands, six or eight in number. 



The mature glands (figs. 2 and 7) extend deep down into the inner loose layer of the 

 corium and when fully developed reach an immense size. Usually longer than their 

 breadth, they may be perfectly round or somewhat flattened from above (epidermalwanl) 

 downwards. The largest acini which we have seen had an average length or depth of 

 3 millimeters and an average breadth of 2 millimeters. The wall of the gland is formed of 

 an homogeneous matrix, in which is embedded a thick layer of spindle-shaped cells, which 

 layer surrounds the entire gland (fig. 8). Most authors who have written on the subject 

 of batrachian poison-glands are united in considering the spindle cells to be fibers of non- 



