ON ACTIVK MOLECULES. 4H1 



ever, ])VOcee(lccl merely from defective mimipulatioii ; for I 

 have since readily obtained them from all these bodies : at 

 the same time I ought to notice that their existence in 

 sulphur was })reviously mentioned to me by my friend Mr. 

 Lister. 



In prosecutinji; the inquiry subsequent to the publication 

 of my Observations, I have chiefly employed the simple 

 microscope^ mentioned in the Pampldet as having been made 

 for me by My. Dollond, and of which the three lenses that 

 T have generally used, arc of a 10th, OOth, and 70th of an 

 inch focus. 



i\Iany of the observations have been repeated and con- 

 firmed with other simple microscopes having lenses of simi- 

 lar powers, and also with the best achromatic com])ound 

 microscopes, either in my own possession or belonging to 

 my friends. 



The result of the inquiry at present essentially agrees with 

 that which may be collected from my printed account, p 

 and may be here briefly stated in the following terms ; 

 namely. 



That extremely minute particles of soUd matter, whether 

 obtained from organic or inorganic substances, when sus- 

 pended in pure water, or in some other aqueous fluids, 

 exhibit motions for which I am unable to account, and 

 which from their irregularity and seeming independence 

 resemble in a remarkable degree the less rapid motions of 

 some of the simplest animalcules of infusions. That the 

 smallest moving particles observed, and which I have termed 

 Active Molecules, appear to be spherical, or nearly so, and 

 to be between l-:20,000dth and l-:30,000dth of an inch in 

 diameter ; and that other particles of considerably greater 

 and various size, and either of similar or of very diftercnt 

 ■ figure, also ])resent analogous motions in like circum- 

 stances. 



I have formerly stated my belief that these motions of 

 the ])articles neither arose from currents in the fluid con- 

 taining them, nor depended on that intestine motion which 

 may be supposed to accompany its evaporation. 



These causes of motion, however^ either singly or combined 



31 



