036 THE MICROSCOPE. 



from this, found upon the body of the very poor and dirty t 

 known as the body or crab-louse. Leeuwenhoek carried his 

 researches on the habits of these insects further than most 

 investigators, even allowing his zeal to overcome his disgust 

 for such creatures as the louse. In describing its mode of 

 taking food, &c., he observes : " In my experiments, 

 although I had at one time several on my hand drawing 

 blood, yet I very rarely felt any pain from their punctures ; 

 which is not to be wondered at, when we consider the 

 excessive slenderness of the piercer ; for, upon comparing 

 this with a hair taken from the back of my hand, I judged, 

 from the most accurate computation I could form by the 

 microscope, that the hair was 700 times larger than this 

 incredibly slender piercer, which consequently by its 

 punctures must excite little or no pain, unless it happens 

 to touch a nerve. Hence I have been induced to think 

 that the pain or uneasiness those persons suffer who are 

 infested by these creatures, is not so much produced from 

 the piercer as from a real sting, which the male louse 

 carries in the hinder part of his body, and uses as a 

 weapon of defence." He found, from experiments made 

 to ascertain the possible increase of these pests, that from 

 two females he obtained in eight weeks the almost in- 

 credible number of 10,000 eggs. 



The Itch-insect, Acarus scabiei (fig. 290, No. 3, magni- 

 fied 350 diameters). Dr. Bononio was among the first to 

 detect the parasitic character of the disease known as the 

 itch. On turning out one of the pustules, or little blad- 

 ders, from between the fingers, with the points of very 

 fine needles, under the microscope, a minute animal was 

 discovered, very nimble in its motion, covered with short 

 hairs, having a short head, a pair of strong mandibles or 

 cutting jaws, and eight legs, terminating in remarkable 

 appendages, each provided with a sucker and setae. 



It has no eyes ; but when disturbed it quickly draws in 

 its head and feet, and then somewhat resembles the tor- 

 toise in appearance, its march is precisely that of the tor- 

 toise. It usually lays sixteen eggs, which are carefully 

 deposited in furrows under the skin, and ranged in pairs j 

 these hatch in about ten days. 



To find the itch-insect, the operator must examine care- 



