34 Observations on Parasites and Parasitic Diseases 



its agility and strength, being capable, according to computation, 

 of leaping fully two hundred times its own length, and of moving 

 a weight which many times exceeds that of its body. 



Fleas infest various mammals and also birds, but are rarely met 

 with on any domesticated animal, excepting the pig, the dog, and 

 the cat. Poultry and pigeons are likewise subject to fleas, and 

 occasionally they are present in very large numbers in old straw 

 or thatch, and are thus brought into the cattle-sheds and pig- 

 cotes of the farm, or even into the house itself. In a case which 

 came under our notice some years since, we were enabled to trace 

 their presence to the erection of some pigsties with old building- 

 materials, and the thatching of them with old straw. They 

 were erected in a meadow near to the premises, and proved 

 to be so infested with fleas that the proprietor at last wisely 

 determined not only on pulling them down, but on setting fire to 

 the whole of the materials. By these means alone he succeeded 

 in freeing his dwelling-house, and also that of a neighbour, from 

 these troublesome parasites. 



Besides instances of this kind, it has not unfrequently hap- 

 pened that extraordinary visitations of fleas have taken place in 

 particular districts, the origin of which could not be traced. We 

 were recently informed of such a case ; too late, however, even 

 for an examination of specimens to determine the variety to 

 which the fleas belonged. The visitation assumed such propor- 

 tions that not only the yards and buildings but the adjacent fields 

 also swarmed with these troublesome insects. After remaining 

 for three or four weeks, to the great discomfort of the family as 

 well as of the animals on the farm, they gradually disappeared, 

 without any means for their eradication having been adopted. 



Naturalists place the flea in the order Diptera, sub-order 

 Aphaniptera — sheath-winged and hopping diptera — and family 

 Pulicida, of which it constitutes the only genus, although the 

 varieties are numerous, amounting, according to some authors, 

 to as many as twenty-five. The insect undergoes a complete 

 metamorphosis, analogous in every respect to that of moths or 

 butterflies. The female flea of man — Pulex irritans — is said to 

 lay about a dozen eggs at a time, which are ovoid in form and 

 comparatively large, bearing a strong resemblance in these par- 

 ticulars to the egg of the dog-flea. At first the eggs are of a 

 whitish colour, but they soon acquire a dark hue. 



The egg of the dog-flea, see Fig. 1, A., which may be taken 

 as a type of the class, gives birth after a very short period 

 to a larva, which is long and slender, somewhat resembling 

 a worm in its form, and differing in no essential particular 

 from the larva of the Pulex irritans. The larva. Fig. 1, B, 

 as will be observed in the illustration, consists of fourteen 



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