260 RAINEY, ON THE STRUCTURE OF THE 



ness in different parts of the animal, but present, I believe, in 

 all. This part of the dermis is composed of irregularly- 

 shaped masses of a semitransparent and highly-refractive 

 material (fig. 4), looking like broken fragments of crystal or 

 glass, lodged in cellular depressions of the true skin. Where 

 the secreting follicles are situated, this earthy matter is placed 

 superficial to them, so that their openings have to penetrate a 

 layer of earthy substance, in order to reach the surface of the 

 dermis. This part of the skin, when acted upon by acids, under 

 the microscope is seen to effervesce briskly, and after all the 

 earthy material is dissolved out, a membranous or animal 

 basis is left. Probably this part of the skin in the Toad is 

 analogous to the scaly covering of the Chelonian reptiles. 

 According to Dr. Davy's analysis of the skin of the toad, it 

 contains phosphate and carbonate of lime, and carbonate of 

 magnesia. No organs like those which I have described as 

 the cutaneous follicles of the Toad, exist in the integument of 

 the Frog or Water-newt. In these reptiles the skin is much 

 more simple, and all the vessels supplying it go into the com- 

 mon superficial plexus of ..the dermis. I have not examined 

 the skins of those lizards whose habits resemble those of the 

 toad, for the purpose of determining whether the same kind 

 of follicles exist also in them. 



With respect to the chemical and physical properties of the 

 secretion of the Toad's skin, Dr. Davy observes, in a paper 

 contained in the ' Philosophical Transac tions,' for 1826, that 

 the greater part of it is soluble both in alcohol and in water ; 

 that the substance obtained by evaporation, both of the 

 aqueous and alcoholic solution, is slightly yellow, and has a 

 faint and peculiar smell ; that when heated it readily melts, 

 and burns with a bright flame, but without emitting an am- 

 moniacal odour ; also that the secretion is slightly bitter, 

 and very acrid, acting on the tongue like the extract of 

 aconite, and even occasioning a smarting sensation when 

 applied to the skin of the hand, which lasted for two or three 

 hours ; that it does not affect the colour of litmus, or tur- 

 meric paper. This secretion, though possessed of these 

 decidedly acrid properties, even in a much greater degree than 

 the poison of the most venomous snakes, was not found by 

 Dr. Davy to produce any injurious effects when applied to a 

 wound on a Chicken, made with a lancet dipped in it ; and 

 hence it seems to be endowed merely with irritating qualities, 

 and not to possess the venomous properties attributed to it by 

 the French investigators. 



The experiments which I have performed upon living ani- 

 mals with this secretion, have in no instance agreed in their 



