VOL. XXIII.] PHILOSOPHICAL TRANSACTIONS. 3 



gnawing and working in with their body they cause a most troublesome itching, 

 till they are got quite under the cuticula, and then it is easy to see how they 

 make their way from place to place by their biting and eating ; a single one 

 sometimes making several pustules, of which I have often found 2 or 3 toge- 

 ther, and for the most part very near each other. 



With great earnestness I examined whether these animalcules laid eggs, and 

 after many inquiries, at last by good fortune, while I was drawing the figure of 

 one of them by a microscope, from the hinder part I saw drop a very small and 

 scarcely visible white eggj almost transparent and oblong, like the seed of a pine 

 apple, as represented in fig. 3 and 4. I often fonnd these eggs afterwards, from 

 which, no doubt, these creatures are generated, as all others are, that is from a 

 male and female, though I have not yet been able by any difference of figure to 

 distinguish their sex.* 



From this discovery it inay be no difficult matter to give a more rational 

 account of the itch, than authors have hitherto delivered us. It being very 

 probable, that this contagious disease owes its origin neither to the melancholy 

 humour of Galen, nor the corrosive acid of Sylvius, nor the particular ferment 

 of Van Helmont, nor the irritating salts in the serum or lympha of the mo- 

 derns, bnt rather to the continual biting of these animalcules in the skin, by 

 means of which some portion of the serum oozing out through the small aper- 

 tures of the cutis, little watery bladders are made, within which the insects 

 continuing to gnaw, the infected are forced to scratch, and by scratching in- 

 crease the mischief, and thus renew the troublesome work, breaking not only 

 the little pustules, but the skin too, and some little blood vessels, and so mak- 

 ing scabs, crusty sores, and such like foul symptoms. 



From hence we come to understand how the itch proves to be a distemper so 

 very catching, since these animals by a simple contact can easily pass from one 

 body to another, their motion being wonderfully swift, and crawling, as well on 

 the surface of the body as under the cuticula, being very apt to stick to every 

 thing that touches them, and a very few of them being once lodged, they multi- 

 ply apace by the eggs which they lay. Nor is it any wonder that this infection 

 is propagated by means of sheets, towels, handkerchiefs, gloves, &c. used by 

 itchy persons, it being easy enough for some of these creepers to be lodged in 

 such things as these ; and indeed, I have observed that they will live out of the 

 body for 2 or 3 days. 



Nor in the last place shall we be at a loss to know the reason of the cure of 

 this malady by lixivial washes, baths, and ointments made up with salts, sul- 



* The animalcules here described belong to the Linnaean genus acarus. 



B 2 



