071 Active Molecules. 315 



•satisfied now that such is the fact. But even had the unifor- 

 mity of the Molecules in those two points been absolutely 

 established, it did not necessarily follow, nor have I any where 

 stated, as has been imputed to me, that they also agreed in all 

 their other properties and functions. 



I have remarked, that certain substances, namely, sulphur, 

 resin, and wax, did not yield active particles, which, however, 

 proceeded merely from defective manipulation ; 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 pre- 

 viously mentioned to me by my friend Mr Lister. 



In prosecuting the inquiry subsequent to the publication of 

 my Observations, I have chiefly employed the simple micro- 

 scope mentioned in the Pamphlet, as having been made for 

 me by Mr Dollond, and of which the three lenses that I have 

 generally used, are of a 4Qth, 60th, and 70th of an inch focus. 



Many of the observations have been repeated and confirm- 

 ed with other simple microscopes having lenses of similar 

 powers, and also with the best achromatic compound micro- 

 scopes, 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, and 

 may be here briefly stated in the following terms, namely. 



That extremely minute particles of solid matter, whether ob- 

 tained from organic or inorganic substances, when suspended 

 in pure water, or in some other aqueous fluids, exhibit mo- 

 tions for which I am unable to account, and which from their 

 irregularity and seeming independence resemble in a remarka- 

 ble degree the less rapid motions of some of the simplest ani- 

 malcules of infusions. That the smallest moving particles ob- 

 served, 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 par- 

 ticles of considerably greater and various size, and either of 

 similar or of very different figure, also present analogous mo- 

 tions in like circumstances. 



I have formerly stated my belief that these motions of the 

 particles neither arose from currents in the fluid containing 



