22 MONOGRAPHIA 



an hundred males and as many females, and that this young 

 brood in 18 days' time are grown to a size to propagate 

 their kind, and that each of those young females in the 

 space of 12 days more lays an hundred eggs, and from 

 which in six days time other young lice are produced; upon 

 this supposition the number of lice springing from two 

 females will amount to ten thousand. Thus it appears that 

 two females may in eight weeks time be grandmothers, and 

 see 10,000 lice of their own offspring, which unless reduced 

 to actualdemonstration would seem incredible; and who 

 can tell whether in the heat of summer these creatures may 

 not breed in half the time I have mentioned." Hook's 

 Leeuwenhoek, II. pp. 164 to 169. 



The precise use of these creatures in the economy of the 

 universe is not very easy to define, and although I cannot 

 go so far as with Linne to give the louse full credit of pre- 

 serving full-fed boys from coughs, epilepsy, &c. yet I do 

 think it probable they may be conducive to health, in a 

 certain degree, by promoting cleanliness ; for were it not 

 for the great increase which soon takes place, if a colony are 

 allowed undisturbed possession, there are individuals, pro- 

 bably, who are so lost to all sense of decency, that they 

 would never clean themselves at all. But by means of this 

 peculiar stimulus, it becomes absolutely necessary to have 

 a battu now and then, in order to prevent a redundance of 

 the population, and in this view I am not alone, for Serenus 

 says, 



" See Nature kindly provident ordain 

 Her gentle stimulants to harmless pain, 

 Lest man, the slave of rest, should waste away, 

 In torpid slumber life's important day." 



Therefore, however disgusting and loathsome these insects 

 may be to one portion of mankind, we must not on that 



