SOURCE OF TUE STTSQ. 287 



, in tlie road from Carthagena to Honda, while we 

 were dissecting a crocodile eleven feet long, the smell of 

 which infested all the surrounding atmosphere. The Indians 

 much commend the fumes of burnt cow-dung. When the 

 wind is very strong, and accompanied by rain, the mosquitos 

 disappear for some time: they sting most cruelly at the 

 approach of a storm, particularly when the electric explo- 

 sions are not followed by heavy showers. 



Anything waved about the head and the hands contri- 

 butes to chase away the insects. " The more you stir your- 

 self, the less you will be stung," say the missionaries. The 

 zancudo makes a buzzing before it settles ; but, when it 

 has assumed confidence, when it has once begun to fix its 

 sucker, and distend itself, you may touch its wings without 

 its being frightened. It remains the whole time with its 

 two hind legs raised; and, if left to suck to satiety, no 

 swelling takes place, and no pain is left behind. We often 

 repeated this experiment on ourselves in the valley of the 

 Rio Magdalena. It may be asked whether the insect 

 deposits the stimulating liquid only at the moment of its 

 flight, when it is driven away, or whether it draws the 

 liquid up again when left to suck undisturbed. I incline to 

 this latter opinion; for on quietly presenting the back of 

 my hand to the Culex cyanopterus, I observed that the 

 pain, though violent in the beginning, diminishes in pro- 

 portion as the insect continues to suck, and ceases altogether 

 when it voluntarily flies away. I also wounded my skin 

 with a pin, and rubbed the pricks with bruised mosquitos, 

 and no swelling ensued. The irritating liquid, in which 

 chemists have not yet recognized any acid properties, is 

 contained, as in the ant and other hymenopterous insects, 

 in particular glands ; and is probably too much diluted, and 

 consequently too much weakened, if the skin be rubbed 

 with the whole of the bruised insect. 



I have thrown together at the close of this chapter all 

 we learned during the course of our travels on phenomena 

 which naturalists have hitherto singularly neglected, though 

 they exercise a great influence on the welfare of the inha- 

 bitants, the salubrity of the climate, and the establishment 

 of new colonies on the rivers of equinoctial America. I 

 might justly have incurred the charge of having treated 



