HISTOLOGY OF THE POISON-GLANDS OF BUFO AGUA. 77 



shown that this homogeneous liquid is not merely a diluting fluid, hut the- most virulent 

 poison the toad excretes. 



Enough is known of the physical and toxicologic properties of this parotid secretion to 

 make it plain how deadly and effective a defensive weapon it would be against an animal 

 which had seized upon the toad as a prey. The nauseous bitter taste of the crude secretion 

 and the immediate and intense salivation which follows the contact of even the smallest 

 amount of it with an unprotected oral mucous membrane would insure the immediate 

 release of the toad from an enemy's grip. Nor is this all, for should the venom come in 

 contact with the mucosa of an empty stomach, violent retching and vomiting results. 

 "0.1 gm. in a capsule given by mouth to a fasting dog weighing 5.8 kg., was followed in 10 

 minutes by the emesis of a clear bile-stained fluid, containing most of the poison; vomiting 

 followed for 20 minutes." (Abel and Macht, loc. cit., p. 326.) 



Even more deadly is the result of an intra-venous exhibition of the venom. Abel and 

 Macht (p. 326) say: "Injected intravenously into a large cat a quantity of the emulsion 

 containing less than 0.020 gram of the crude dried venom induced a tremendous rise of 

 blood-pressure, followed immediately by a fall, due to a sudden and complete standstill of 

 the heart," 



The speed and the deadly effect of the toad venom have long been known to some of 

 the South American Indians, who have used the secretion as a poison to coat the tips of 

 darts and arrows. 



THE SKIN. 



Before describing the histology of the poison-glands themselves, in order that their 

 structure and relations may be understood, a short description of the epidermis from which 

 they arise and the cutis vera in which they are embedded is necessary. 



THE EPIDERMIS. 



In celloidin sections it may be seen that the epidermis is composed of a stratified 

 squamous epithelium, having from 4 to 8 layers of living cells (figs. 4 to 7) . The layer nearest 

 the cutis vera seems to compose the stratum germinativum and in this layer the cells are 

 high-columnar in form. The cell-body gradually flattens as the higher strata are reached 

 and the nuclei of the cells in the higher layers become larger and less chromatic, with a 

 fine-tin eaded open-meshed network, in contrast to the small dark-staining nuclei of the 

 germinating stratum. Some of the cells in the transitional layers have in their cytoplasm 

 a few scattered granules of pigments, probably eleidin, and fine protoplasmic spines or 

 prickles show very clearly. After the cells pass through the transitional stage the nuclei are 

 lost from the cytoplasm and the epithelium becomes the lifeless molt which is periodically 

 cast off by the toad. 



The thickness of the epidermis is very variable throughout the body, but in the parotid 

 region there is a noticeable thickening about the poison-gland orifices. These thickenings, 

 which are due both to an hypertrophy of the individual epithelial cells and an increase in 

 their number, show in sections as little epithelial mounds or hillocks on either side of the 

 duct opening, midway between it and the mouth of the next duct. From these little mounds 

 the epidermis slopes gradually, becoming thinner as it descends to dip suddenly into the 

 mouth of the gland-duct, the abrupt descent into the duct-lumen being usually marked, as 

 Muhse has stated, by a second thickening of the epidermis. The small "mucous" glands 

 cause no disturbance in the epithelium. 



At frequent intervals one-celled glands, the so-called beaker -cells, may be found, 

 which are entirely in the epidermis. They are very small and are seen between the 



