ACARINA PARASITES. 455 



and the instrument of torture with which it pierces the 

 flesh and draws the blood. To the fore part of its body 

 six legs are affixed, having each five joints, terminated 

 by two unequal hooks; these, with other portions, are 

 covered with short hairs. Around the outer margin of 

 the body may be seen small circular dots, the breathing 

 apertures, with which all the class are freely provided, 

 rendering them very tenacious of life, and difficult to kill. 

 There is another louse, rather differing in its characteristics 

 from this, formed about the body of the very poor and dirty, 

 called the body or crab-louse. Leeuwenhoek carried hi? 

 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 

 incredible 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 vermin, that 

 from two females he obtained in eight weeks the incredible 

 number of 10,000 eggs. 



The scab in sheep is caused by a family of Acarina, 

 the Sarcoptes scabiei, which also produces the itch in the 

 human being, and lately discovered to be the cause of mange 

 in the dog. In one pustule from a dog, suffering from 

 this disease, as many as thirty or forty of the parasites 

 were found. This is the genus Demodex of Professor Owen, 

 who classes them with Arachnida. 



The Itch-insectj ftarcoptes scabiei (fig. 220, No. 3, magni- 



