THE LOUSE. 



457 



legs, consisting of six joints, covered also with 

 bristly hairs ; the ends of the legs are armed 

 with two smaller and larger ruddy claws, serv- 

 ing these insects as a finger and thumb, by 

 which they catch hold of such objects as they 

 approach : the end of the body terminates in a 

 cloven tail, while the sides are all over hairy ; 

 the whole resembling clear parchment, and, 

 when roughly pressed, crackling with a noise. 

 When we take a closer view, its white 

 veins and other internal parts appear, as like- 

 wise a most wonderful motion in its intestines, 

 from the transparency of its external covering. 

 When the louse feeds, the blood is seen to 

 rush, like a torrent, into the stomach ; and its 

 greediness is so great, that the excrements con- 

 tained in the intestines are ejected at the same 

 time, to make room for this new supply. 



The louse has neither beak, teeth, nor any 

 kind of mouth, as Dr Hooke described it, for 

 the entrance into the gullet is absolutely closed. 

 In the place of all these, it has a proboscis or 

 trunk : or, as it may be otherwise called, a 

 pointed hollow sucker, with which it pierces 

 the skin, and sucks the human blood, taking 

 that for food only. The stomach is lodged 

 partly in the breast and back ; but the great- 

 est portion of it is in the abdomen. When 

 swollen with blood, it appears of a dark brown 

 colour, which is visible through the skin ; and 

 is either a faint red, or a full or bright brown, 

 as the contents of the stomach are more or less 

 changed. When it is empty, it is colourless ; 

 but when filled, it is plainly discernible, and 

 its motion seems very extraordinary. It then 

 appears working with very strong agitations, 

 and somewhat resembles an animal within an 

 animal. Superficial observers are apt to take 

 this for the pulsation of the heart : but if the 

 animal be observed when it is sucking, it will 

 then be found that the food takes a direct pas- 

 sage from the trunk to the stomach, where the 

 remainder of the old aliment will be seen mix- 

 ing with the new, and agitated up and down 

 on every side. 



If this animal be kept from food two or 

 three days, and then placed upon the back of 

 the hand, or any soft part of the body, it will 

 immediately seek for food ; which it will the 

 more readily find, if the hand be rubbed till it 

 grows red, The animal then turns its head, 

 which lies between the two fore-legs, to the 

 skin, and diligently searches for some pore : 

 when found, it fixes the trunk therein, and soon 

 the microscope discovers the blood ascending 

 through the head, in a very rapid, and even 

 frightful stream. The louse has at that time 

 sufficient appetite to feed in any posture ; it is 

 then seen sucking with its head downward, 

 and its tail elevated. If, during this opera- 

 tion, the skin be drawn tight, the trunk is 

 bound fast, and the animal is incapable of dis- 



VOL. II. 



engaging itself ; but it more frequently suffers 

 from its gluttony, since it gorges to such a de- 

 gree, that it is crushed to pieces by the slight- 

 est impression. 



Whether lice are distinguished by the parts 

 of generation into males and females is not yet 

 discovered : Swammerdam is inclined to think 

 that they are hermaphrodites, having found an 

 ovary in all those he examined ; and he dis- 

 sected not less than forty-two. In one of 

 these animals were found ten large eggs ; and 

 forty-four smaller, that were not yet come to 

 their full perfection. 



There is scarce any animal that multiplies 

 so fast as this unwelcome intruder. It has been 

 pleasantly said, that a louse becomes a grand- 

 father in the space of twenty- four hours : this 

 fact cannot be ascertained ; but nothing is more 

 true than that the moment the nit, which is no 

 other than the egg of the louse, gets rid of its 

 superfluous moisture, and throws off its shell, 

 it then begins to breed in its turn. Nothing 

 so much prevents the increase of this nauseous 

 animal as cold and want of humidity ; the nits 

 must be laid in a place that is warm, and mo- 

 derately moist, to produce any thing. This is 

 the reason that many nits laid on the hairs in 

 the night-time, are destroyed by the cold of the 

 succeeding day; and so stick for several 

 months, till they at last come to lose even their 

 external form. 



The louse is found upon every part of the 

 human body : but particularly in the heads of 

 children. 1 Those found upon the miners in 



1 All lice live on blood, some on that of man, others on 

 that of quadrupeds. They suck it with their proboscis, 

 which is hardly ever perceived, unless it be in action. 

 There is no quadruped which has not its particular louse, 

 and some nourish several. Man, as we have already 

 seen, is attacked by three species. 



Swammerdam, who has given us the anatomy of the 

 human louse, was unable to discover any male among 

 those which he examined. He always found in them 

 an ovary; which occasioned him to suspect that they 

 were hermaphrodites. But the observations of Leeuwen. 

 hock, differ much from those of that author. He has 

 observed individuals among these insects provided with 

 all the parts which characterize the male sex, and he 

 has given the figures of those parts. The same author 

 has also discovered in those which he regards as males, 

 a recurved sort of sting, situated under the abdomen, 

 with which, according to him, they can prickle. He 

 believes that the great itching which they occasion pro- 

 ceeds from the pricking of this sting, having remarked 

 that the introduction of their proboscis into the flesh 

 produces scarcely any sensation, unless perchance that 

 it touch on any of the nerves. Degeer tells us, that he 

 has seen a similar sting situated at the end of the abdo- 

 men in several human lice as well those of the body, as 

 of the head. The individuals, which according to the 

 opinion of Leeuwenhock are the males, have, according 

 to Degeer, the end of the abdomen rounded, whereas 

 the females, or those which have no sting, have it emar- 

 giriated. M. Latreille has also observed, very distinctly 

 in a great number of individuals, the sting, or at least 

 the conical and scaly point of which the aforesaid authors 

 have made mention. 



SB 



