164 Mr. Brown's Additional Remarks on Active Molecules. 



inversion of the experiment ; for by mixing a very small pro- 

 portion of oil with the water containing the particles, micro- 

 scopic drops of oil of extreme minuteness, some of them not 

 exceeding in size the particles themselves, will be found on the 

 surface of the drop of water, and nearly or altogether at rest ; 

 while the particles in the centre or towards the bottom of the 

 drop continue to move with their usual degree of activity. 



By means of the contrivance now described for reducing 

 the size and prolonging the existence of the drops containing 

 the particles, which, simple as it is, did not till very lately occur 

 to me, a greater command of the subject is obtained, sufficient 

 perhaps to enable us to ascertain the real cause of the motions 

 in question. 



Of the few experiments which I have made since this man- 

 ner of observing was adopted, some appear to me so curious, 

 that I do not venture to state them until they are verified by 

 frequent and careful repetition. 



1 shall conclude these supplementary remarks to my former 

 Observations, by noticing the degree in which I consider those 

 observations to have been anticipated. 



That molecular was sometimes confounded with animalcular 

 motion by several of the earlier microscopical observers, ap- 

 pears exti'emely probable from various passages in the writings 

 of Leeuwenhoek, as well as from a very remarkable Paper by 

 Stephen Gray, published in the 19th volume of tlie Philoso- 

 phical Transactions. 



Needham also, and Buffon, with whom the hypothesis of 

 organic particles originated, seem to have not unfrequently 

 fallen into the same mistake. And I am inclined to believe 

 that Spallanzani, notwithstanding one of his statements re- 

 specting them, has under the head of Animaletti d'ultimo or- 

 dine included the active Molecules as well as true Animalcules. 



I may next mention that Gleichen, the discoverer of the 

 motions of the Particles of the Pollen, also observed similar 

 motions in the particles of the ovulum of Zea Mays. 



Wrisberg and Muller, who adopted in part Buffon's hypo- 

 thesis, state the globules, of which they suppose all organic 

 bodies formed, to be capable of motion ; and Muller distin- 

 guishes these moving organic globules from real Animalcules, 

 with which, he adds, they have been confounded by some 

 very respectable observers. 



In 1814 Dr. .James Drummond, of Belfast, published in tlie 

 7th volume of the Transactions of the Royal Society of Edin- 

 burgh, a valuable Paper, entitled " On certain Appearances 

 observed in the Dissection of the Eyes of Fishes." 



In this Essay, which I regret I was entirely unacquainted 



with 



