oii EVENINGS AT THE MIOKOSClil'K. 



tlioy possess during tlio lil'o o( tlieir owners. It- is, 

 indeed, one of the most inslruelJNc niiMles of using lliis 

 wonder-working- instrnnient to look tln-ongli it at liv- 

 ing strnetnres, and ^vat(■ll the difl'erent processes of lilb 

 as they arc carrirtl on nnder onr eyes. Nor is this at 

 all dilHenlt to acH'oiiiplisii ; for a larij,e number of 

 animals are so small that avc^ ean easily jmt them upon 

 tlic stage of the mierosco]ie, and withal so transpai'ent 

 that their integuments and various tissues ofier little 

 or no impediment to our diseeriiing the Ibrms and 

 movements of the eontuinetl visc^ei-a. And in eases 

 M'hcro the entire animal is too large to be viewed mi- 

 croscopically as a whole, it sometimes happens that, by 

 a little contrivance, we ean so secure the creature as 

 to look, without interruption, on et'rtain jwiia of the 

 body which afford the recpiisite minuteness and trans- 

 parency. 



I have hero a living Frog. You perceive that the 

 web which coiineets the toes is exceedingly thin and 

 ti'anslucent, yet arteries and veins meander through its 

 delieate tissues, which are then clothed on both surfaeos 

 with the conimon skin. But you ask how we can in- 

 duce the Frog to bo so polite as to hold his paw up and 

 keep it steady for our scientific investigation. We will 

 manage that without difficulty. 



Most microscopes are i'urnished (among their acces- 

 sory apparatus) with what is called a frog-plate, ]ii-o- 

 vided for this very demonstration. Here is mine. It 

 is a thin plate of brass, two inches and a half broad and 

 seven long, with a number of small holes piei'ced 

 through it along the margins, and a large oi-ifice near 

 one end, which is (covered with a plate of glass. This 

 is to be Froggy's bed during the operation, for we 



