Prof. H. Karsten on Rhynchoprion penetrans. 297 



is not pressed or scratched. The particular state of the skin as 

 regards irritability will also have its influence, as also the greater 

 or less activity of the skin. It is true that the inhabitants of 

 Caracas have also remarked that, of newly arrived colonists, the 

 French, like the negroes, suffer particularly from the parasitic 

 flea. 



The Nigua is a parasite only during one period of its life; 

 for the impregnated female alone bores into the skin of warm- 

 blooded animals : the unfecundated females and the males do 

 not live parasitically. The dark brown colour of the contents 

 of the stomach in the animals which are found running about 

 indicates that, like the allied Fleas, they live on blood. 



The true colour of the body of the free-living Niguas (leaving 

 out of consideration the dark colour of the contents of the 

 stomach) is yellowish; I have never seen a brown or black R. 

 penetrans, such as are mentioned by Ulloa, Auteroche, and many 

 others. The dilated bodies of the Niguas which had established 

 themselves under my own toe-nails, and more rarely on other 

 parts of the skin, as also of those which I observed on other 

 people and on animals, were of a more or less pure white co- 

 lour; those derived from the skins of negroes appeared grey — 

 probably only influenced by the pigment existing there. No 

 differences of form could be detected. 



From its light colour, the size of the Nigua has been greatly 

 underrated by most describers ; for it measures, on the average, 

 1 millim. (half, or more than half, the size of the common Flea). 

 The males and females are at first of the same size, and it is 

 only during the endoparasitic life of the fecundated female that 

 its body enlarges to the extraordinary diameter of 5 millim. 



As long as the pregnant female remains in the skin undis- 

 turbed by pressure or rubbing, it produces, as far as my expe- 

 rience goes, no further perceptible inconvenience ; it grows to 

 the size above mentioned, and in this condition remains long 

 without alteration. The inconsiderable inflammation, exciting 

 a slight tickling sensation, which is produced in the skin by the 

 assimilating animal, is greatly increased by any irritation of the 

 part affected, and might probably, in bad constitutions, give rise 

 to those destructive effects which have been cited by various 

 writers, and which I have also heard spoken of. I have fre- 

 quently seen young negroes with purulent feet destitute of 

 toes, limping about upon their heels, who indicated the Niguas 

 as the cause of their sufferings. Consequently it is possible 

 that there may be some truth in the narrative of Walton, cited 

 by Kirby and Spence, of the capuchin who had to pay with his 

 foot for his desire to make this animal known in Europe. 

 There is no doubt that negroes are often attacked by tetanus 



