538 LIQUID PARTS OF ANIMALS. 



tention ; because it is only from such an investigation that we 

 can hope to explain the fatal changes which they induce on the 

 animal economy, or to discover an antidote sufficiently powerful 

 to counteract their baneful influence. Unfortunately the task is 

 difficult, and perhaps surpasses our chemical powers. For the 

 progress already made in the investigation, we are indebted 

 chiefly to the labours of Fontana. 



1. The poison of the viper is a yellow liquid, which lodges in 

 two small vesicles in the animal's mouth. These communicate 

 by a tube with the crooked fangs, which are hollow and termi- 

 nate in a small cavity. When the animal bites, the vesicles are 

 squeezed, and the poison forced through the fangs into the wound. 

 This structure was partly observed by Redi, an Italian philoso- 

 pher ; and his discoveries were completed and confirmed by the 

 experiments and observations of Francini,* Tysson,f Mead,| and 

 Fontana. 



This poisonous juice occasions the fatal effects of the viper's 

 bite. If the vesicles be extracted, or the liquid prevented from 

 flowing into the wound, the bite is harmless, If it be infused into 

 wounds made by sharp instruments, it proves as fatal as when 

 introduced by the viper itself. Some of the properties of this 

 liquid were pointed out by Mead ; but it was Fontana who first 

 subjected it to a chemical examination, sacrificing many hundred 

 vipers to his experiments. The quantity contained in a single 

 vesicle scarcely exceeds a drop. 



It has a yellow colour, has no taste ; but when applied to the 

 tongue occasions numbness. It has the appearance of oil be- 

 fore the microscope, but it unites readily with water. It pro- 

 duces no change on vegetable blues. 



When exposed to the open air, the watery part gradually eva- 

 porates, and a yellowish-brown substance remains, which has the 

 appearance of gum-arabic. In this state it feels viscid like gum 

 between the teeth ; it dissolves readily in water, but not in alco- 

 hol ; and alcohol throws it down in a white powder from water. 

 Neither acids nor alkalies have much effect upon it. It does not 

 unite with volatile oils nor sulphuret of potash. When heated 

 it does melt, but swells, and does not inflame till it has become 

 black. These properties are similar to the properties of gum, 



* New Abridg. of the Phil. Trans, ii. 8. f PhH- Trans. Vol. xii. 



| Mead on Poisons, p. 35. 



