56 



feet high; and I presume tha.t there would be fully as many on a 

 plum-tree of the same size. Let us suppose that in a particular grouj) 

 of such plum-trees there are, on the average, only 3,000 leaves on 

 each tree fully stocked with young Mites, as calculated above; or, if 

 any leaves are less fully stocked, as many leaves in all as would be 

 equivalent to 3,000 fully-stocked leaves. Then it follows that there 

 need only be 100 plum-trees, each about ten feet high, in the group, 

 to make up the whole number of 300,000 fully-stocked leaves, which, 

 according to the calculation, are required in order to sustain a pop- 

 ulation of young Mites, equal to the very highest estimate that has 

 ever been published of the entire human population of the earth ! 



Now pluck one of the gall-bearing leaves from such a group of 

 100 plum-trees, which might easily grow upon a piece of ground 

 much smaller than a common-sized village lot. Open one of the gall.r 

 on it. Examine its inhabitants with a powerful magnifier. You 

 will see at once, that all this infinite multitude of infinitesimally 

 minute beings are as perfect in every limb, and in every joint of 

 every limb, and probably in every nerve and muscle of their tiny 

 bodies, as the gigantic animal that is watching their operations 

 through a piece of glass. They are all busy. They are all evidently 

 healthy, and happy, and in the full enjoyment of their existence. 

 They contribute in no wise to our pleasures or to our necessities; 

 neither do they molest or trouble us in any Avay whatever. We are 

 separated from them by as wide a gulf, as if they were denizens of 

 the far-away planet Neptune, And yet we fondly dream, in our 

 vainglorious hallucination, that all this vast woi'ld of life and hap- 

 piness—so minute in size, but so inconceivably large in numbers — 

 was created for our sole benefit, and has no right to exist but by our 

 sovereign permission and at our good will and pleasure ! 



All the Mites, however, do not feed upon living vegetable sub- 

 stances, like these gall -makers that I have just been picturing to the. 

 mind of the reader. As with the true Insects, many groups of them 

 feed upon decaying substances, either of animal or vegetable origin, 

 many are Parasites, and many others are Cannibals. For example, 

 the common Cheese-mite, an imported European species, feeds upon 

 decaying cheese, where, when it is once established, it soon multiplies 

 with the most astonishing rapidity. Again : the common Itch, in 

 that two-legged animal that Linnasus designated as Homo sapiens, 

 is caused by a microscopically minute Mite {Acarus scahiei, Linnaeus) 

 burrowing under his skin, and there carrying out^he great Law of 

 Nature, "Increase and multiply and replenish the earth." This 

 species, therefore, is a true Parasite. Again: I have noticed many 



