ACARINA — PARASITES. 329 



five joints, terminated by two unequal hooks ; these, with the 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 this class of animals are 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 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 ex- 

 cessive 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 seven 

 hundred times the size of this incredible slender piercer, which conse- 

 quently 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 hind part -of his body, and uses as a weapon 

 of defence.'' He found from experiments made to ascertain the in- 

 crease of these vermin, that from two females he obtained in eight 

 weeks the incredible number of 10,000 eggs. 



The Itch-insect, Sarcpptes scahiei (Plate XI. No. 3, magnified 350 

 diameters). Dr. Bononio made out the true character of the very 

 troublesome disease known as the itch. Upon examining one of the 

 pustules, or little bladders, from between the fingers, with the points of 

 very fine needles, under the microscope, he perceived a very small ani- 

 mal, very nimble in its motion, covered with short hairs, having a for- 

 midable head with a pair of strong mandibles or cutting jaws, and 

 eight legs, from the extremities of which are appended remarkable 

 feet, each provided with a sucker, by means of which it no doubt sucks 

 or draws its way beneath the skin, having first cut out a small section 

 with its mandibles ; here the insects form a nest, lay eggs, and mul- 

 tiply rapidly, being most diflicult to dislodge. 



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

 parts surrounding each pustule, and he will see a red line or spot com- 

 municating with it ; this part, and not the pustule, must be probed 

 with a fine-pointed instrument j the operator must not be disappointed 



