The little spot around the wound appears as if affected by chloroform.

Fig. 8.-Gnat (culex pipiens) larva and nymph. (Blanchard.

These parasites repay by an unkind action the assistance which they have demanded from us.

Besides the gnats, which belong to the family of Culicidæ, there are also the Ceratopogon, and especially the Simulium molestum, known in North America under the name of Black-flies: "the tormenting black-flies of this country," as the Americans say. Certain Nemocera, known by the name of Rhagio, put to flight both man and animals.

They are very small; they get into the nostrils, and cause animals to become blind by introducing themselves into their eyes. In addition to these hurtful insects, we find others fatal to the life of animals, and which are a real plague in certain countries.

The numerous travellers who have explored the interior of Africa, have almost all spoken to us of a fly which attacks beasts of burden, and kills them in a few hours; this is the Tsetse (Glossina morsitans). More than one expedition has failed on account of this dipterous fly. It was this which obliged Green to abandon his plan of reaching Libebe, by causing him. to lose one after another all his beasts of burden and of draught. The horse, the ox, and the dog are more especially attacked by this terrible fly between the 22nd and 28th degree of longitude, and the 18th and 24th of south latitude. Happily it does not produce any effect

upon man.

There is another fly in Mexico which is dangerous to man; it is known by the name of Musca hominivora, or more correctly, Lucilia hominivora. Vercammer, a military surgeon of the Belgian army, relates that a soldier in Mexico had his glottis destroyed, and the sides and the roof of his mouth rendered ragged and torn, as if a cutting punch had been driven into those organs. This

soldier threw up with his spittle more than two hundred larvæ of this fly. We give below the figure of the larva and of the perfect insect. He had found this man sick in Michoacan, at a height of 1,866 metres, between Mexico and Morelia.

Fig. 9.-Lucilia hominivora.

Fig. 10.-Lucilia hominivora, larva.

My son-in-law, Dr. Vanlair, informs me that citric acid or the juice of lemons is efficacious in destroying these insects. Injections of this acid are thrown into the nasal fossæ.

At Brazil, in the province of Minas Geraes, they give the name of Berne to a fly which attacks man and cattle from the month of November until February. It deposits its eggs in the loins, the arms, the legs, or even the scrotum, without the victims perceiving it, and their presence is first shown by a redness, then by a sensation of itching, and a swelling with the formation of pus.

Among those insects which suck the blood, is one which is known by every one, the Breeze-fly, Tabanus bovinus. Happily it seldom attacks any animals except oxen and COWS. We give a representation of the insect, the parts of the mouth, and one of the antennæ.

In the same order of diptera are found ordinary flies, among which may be easily distinguished the three spe

cies which are here represented, and which differ as much by their external characters as by their mode of life.

Another fly also attacks horses and cattle, and occasionally even man, the Asilus crabroniformis, whose wounds sometimes draw blood. Martins, the birds of the twilight, which fly in flocks above the houses,

describing circles and uttering shrill cries, are usually infested by many vermin, among which we find a fly of

considerable size, which looks much like a spider, the Ornithomya hirundinis. It moves about among the

feathers with astonishing facility, and it is not always confined to the same bird; it quits its host to establish

itself upon another, and sometimes throws itself upon man to suck his blood.

Some years ago these insects penetrated in the middle of the night through the open windows into one of the apartments of the military hospital at Louvain, and the next morning the skin of many of the patients, and especially the bed-linen, were covered with stains of blood. The physicians sent me some of these insects, not knowing whence they had come, nor whether they had been the cause of this annoyance. During the night, these Ornithomyæ had quitted their hosts to attack the soldiers.

One of these insects, the banded Syrphus (Syrphus balteatus), when in the larva state, seizes the rose aphides, and sucks their blood with great eagerness.

But it is not precisely a case of parasitism, when the wounds of soldiers are covered with larvæ, of which there were many sad instances in the Crimean war. There are flies which deposit their eggs in pus, as in