Litter to the Suryeon General of the Army \ accompany ivy ten photoyraphs of certain parasites. 
Army Medical Museum, 
January 10, 1872. 
BRIG ADIEU GENERAL J. K. BARNES, 
Surgeon General, I'. S. Army. 
General: In my letter accompanying certain photographs of the Mosquito, I explained the circum- 
stances under which these representations of subjects so foreign to my ordinary line of work, were produced. 
Ou the present occasion, therefore, I confine myself to a brief description of the photographs herewith 
transmitted. 
No. 1. Bed-bug ( Cimv.e lect alarms') magnified 30 diameters. Negative No. 455, new series. This 
is a hemipterous insect, in which, however, the wings are wanting. The photograph exhibits the numerous 
bristles or hairs with which all portions of the creature arc beset; the six legs with their terminal hooks; 
the small, somewhat quadrate head, deeply sunk in the prothorax ; on eaeh side of the head the four- 
jointed antcume or feelers, (the last joint of the left antenna is broken off); and finally between the 
antennae the jointed beak with which the bug makes its attack upon our flesh. 
No. 2. Head-louse ( Pctlinilus capitis ) magnified 50 diameters. Negative No. 452, new' series. The 
louse, like the bed-bug, is a wingless hemipterous insect. The specimen photographed is a male. The 
picture shows the integument of the insect to be every where beset with short delicate bristles. Each of the 
six legs terminates in a conspicuous claw, admirably formed for grasping the hairs among which it lives. 
Hie head bears two five-jointed antennae between which the mouth-parts terminate in a beak-like sucker. 
1 his latter, however, is fleshy and retractile and in the specimen represented, being drawn within the 
head, is not seen On the margins of the abdominal segments are the circular orifices of the tracheae or 
Ineathing tubes, which in insects convey air to all portions of the body and act instead of luugs. Some 
parts of the abdomen are so transparent that the larger of these tracheae are shown in the photograph. 
No. o. (. iab-lpuse ( Phthimus pubis ) magnified 80 diameters. Negative No. 510, new scries. In 
this insect which is very similar in structure and habits to the head-louse, the sucking beak is also retractile. 
Ihc specimen, which represents a female insect, is, however, so transparent that the outlines of the sucking- 
apparatus can be seen in the photograph. Short anteunae project on each side of the head. The anterior 
legs on each side are comparatively slender, the four others terminate in the great crab-like claws from 
which the insect derives its name. Round openings into the tracheae such as are shown in the photograph 
of the head-louse can be seen near the margin of the thoracic, as well as of the abdominal segments, and in 
several places the trachea) themselves come into view through the transparent skin. The bristles which 
occur on the abdomen and legs, are more sparsely scattered than on the liead-lousc. 
No. 4. Louse of the dog (Hxmatopinus piliferous) magnified 80 diameters. Negative No. 515, 
new series. 1 he general resemblance of this parasite to the human head-louse will at once arrest 
attention. Aside, however, from technical distinctions, the swollen abdomen of the dog-louse aud the 
great number of stout bristles with which it is beset will serve to distinguish it. It may here be mentioned 
as a mattei ot interest that the popular idea that each animal has its own peculiar parasite, which occurs 
on no other creature is not strictly correct. A number of instances are mentioned by Benny* of the 
occurrence ol the same parasite ou several different animals. This would especially appear to be the case 
■'An essay on the British species of parasitic insects. By Henry Denny, London, 1842.— Preface. 
