268 RAINEY, ON THE STRUCTURE OF THE 



this subject so as to lead to the decision of this long-contro- 

 verted question, is to repeat the experiments of these investi- 

 gators under, as nearly as possible, the same circumstances as 

 those under which they were performed, and note carefully 

 the results, still there are some objections to the conclusions 

 to which tliey seem to have arrived, which deserve to be 

 noticed. With respect to the first experiment, as an isolated 

 example, it, in my opinion, proves nothing positive, nor can 

 it have any weight, unless a similar effect can be produced 

 upon the same species of animal whenever the secretion is 

 applied in sufi&cient quantities. The alleged facts of this 

 secretion being, as it were, only a diluted kind of venom, and 

 containing a poison separable by chemical reagents, seem at 

 variance with the nature of organic animal venoms generally, 

 such as that of the Viper, the Bee, &c., which, in their natural 

 state, are sufficiently concentrated to produce the most unequi- 

 vocal effects as animal poisons. Besides, organic poisons of 

 this kind are most probably so easily decomposed, that the 

 chemical means employed to isolate their poisonous principle, 

 could scarcely fail to destroy its specific properties. But 

 before describing the experiments which I have performed 

 with the secretion of the toad's skin, with a view to test the 

 accuracy of the above statements, I will give an account of 

 the structure of the follicles by which it is secreted, this 

 being the especial object of this communication, as .1 am not 

 aware that these organs have ever been described. These 

 bodies (Plate XI., figs. 1 and 2) exist in the form of vascular 

 sacks, of various sizes, but largest about the sides of the head 

 and back ; they are situated in the very substance of the skin 

 of this reptile ; the vessels supplying them are altogether 

 distinct from the capillary network on the surface of the skin, 

 and have an especial arrangement and form of distribution by 

 which their presence can be recognized. These follicles, 

 though sufficiently characteristic, are difficult of demonstra- 

 tion, in consequence of being seen with perfect distinctness 

 only in the skin of the Toad when injected with colouring 

 matter and dried, and afterwards rendered transparent by im- 

 mersion in tur])entine or Canada balsam. This difficulty 

 proceeds from the opacity of the portion of skin situated 

 behind the follicle, preventing, whilst it is wet, the deep part 

 of the follicle from being seen, whilst the cutaneous capillary 

 network conceals the part of it nearest the surface. They are 

 of a globular form when distended, but somewhat flask-shaped 

 when empty (fig. 2). They range from l-50th to l-16th of 

 an inch in diameter. About the centre of the cutaneous sur- 

 face of each follicle there is an opening by which its cavity 



