xl INTRODUCTION. 



though, in order to obtain a greater intensity of colour, I 

 allowed a drop of violet-juice to dry on each plate of the 

 compressorium, so that with a power of 800 diameters, the 

 whole field was of a deep uniform translucent blue — still 

 the ejected wire produced no change of tint. 



Such a test as this is not sufficient to prove that no acid 

 or alkaline property exists in the discharged fluid, and still 

 less that no poisonous fluid at all is effused ; since that 

 most concentrated poison, the venom of the rattlesnake, is 

 said to change vegetable blues to reds, in so slight a degree 

 as to be scarcely perceptible* 



Admitting the existence of a venomous fluid, it is diffi- 

 cult to imagine where it is lodged, and how it is injected. 

 The first thought that occurs to one's mind is, that it is the 

 organic fluid which we have seen to fill the interior of the 

 cnida, and to be forced through the everting tubular ectho- 

 rceum. But if so, it cannot be ejected through the ex- 

 tremity of the ecthorceum, because if this were an open 

 tube, I do not see how the contraction of the fluid in the 

 cnida could force it to evolve; the fluid would escape 

 through the still inverted tube. It is just possible that 

 the barbs may be tubes open at the tips, and that the 

 poison-fluid may be ejected through these. But I rather 

 incline to the hypothesis, that the cavity of the ecthorceum 

 in its 'primal inverted condition while it yet remains coiled up 

 in the cnida, is occupied with the potent fluid in question, 

 and that it is poured out gradually within the tissues of 

 the victim, as the evolving tip of the wire penetrates farther 

 and farther into the wound. 



Perhaps it is not too much to say that the whole range of 

 organic existence does not afford a more wonderful example 

 than this, of the minute workmanship and elaboration of 

 the parts, the extraordinary mode in which certain pre- 

 scribed ends are attained, and the perfect adaptation of the 

 contrivance to the work which it has to do. 



* In a communication made by Dr. M'Donnell to the Royal Society, 

 some experiments were detailed, which had led the observer to believe that 

 electricity was the power in question. In a subsequent paper, however, 

 that gentleman gave up his hypothesis. (Proc. Roy. Soc. Jan. 14, and 

 Nor. 18, 1858.) 





