OF ANIMALCULES. 2/ 



the best instruments with a less amplification than 

 160,000 times (or 400 linear), and when higher powers 

 are used (viz. 800 to 1200 times), it requires consider- 

 able address in the management of the light in order 

 to exhibit it. The best illumination is obtained by 

 condensed lamp-light, with proper stops to limit the 

 quantity, for they are so delicate and transparent, that 

 if much light be admitted they cannot be seen. In the 

 aplanatic engiscope*, with a power of 800 linear, Dr. 

 Ehrenberg, by feeding them on very finely-divided co- 

 louring matter, has been able to discern from two to six 

 spots in them, which, by analogy with the larger infusoria, 

 are stomachs, or digestive cavities. It may also be pre- 

 sumed that they possess, like the larger animalcules, but 

 one orifice or mouth for the reception of food, and that 

 they do not imbibe nourishment by cuticular absorption, 

 as hitherto supposed \ and it may be observed that the 

 coloured points occupy the hinder part. 



In the drawing. Fig. 1, is represented a group of these 

 animalcules, magnified 800 diameters, or 640,000 times, 

 in surface : in some of them are shewn the dots, as seen 

 when they are fed on indigo : in their natural condi- 

 tion they are merely colourless globules. They differ in 

 size from l-24,000th to 1 -9600th of an inch in diameter ; 

 the largest hitherto observed was found at Koliwan; 

 in general they do not exceed 1- 18,000th in diame- 

 ter. They are often so abundant on the surface of in- 



* This instrument is commonly known by the name of achromatic micro- 

 scope. See " Microscopic Cabinet," page 102. 



