Bache.] 1^4 |;April 20, 



minerals of granite. Even a crushed fragment of the Sphynx gave 

 the same results. He tried substances of both aqueous and igneous 

 origin, travertine, stalactites, lava, obsidian, volcanic ashes, meteoric 

 matter, manganese, nickel, plumbago, bismuth, antimony, arsenic, 

 asbestos, actinolite, tremolite, zeolite, and steatite. He tried par- 

 ticles of wood, living and dead, linen, paper, cotton, silk, wool, 

 hair, and muscular fibre that had been exposed to fire under the 

 blowpipe, douched with water, and submitted to immediate exami- 

 nation. The particles from all these substances exhibited as vivid 

 movement after as before they had been so treated. 



Dr. Brown, about twelve months later, went on further to declare, 

 under the head of "Additional Remarks on Active Molecules," 

 tliat : — " 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 obtained from organic or 

 inorganic substances, when suspended 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 independ- 

 ence, 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 Mole- 

 cules, appear to be spherical, or nearly so, and- to be between 

 1-20,000 and 1-30,000 of an inch in diameter; and that othej par- 

 ticles of considerably greater and various size, and either of similar 

 or of very different figure, also present analogous motions in like 

 circumstances. I have formerly stated my belief that these motions 

 of the particles neither arose from currents in the fluid containing 

 them, nor depended on the intestine motion which may be supposed 

 to accompany its evaporation. These causes of motion, however, 

 either singly or combined with others, — as, the attractions and repul- 

 sions among the particles themselves, their unstable equilibrium in 

 tlie fluid in which they are suspended, their hygrometrical or capil- 

 lary action, and in some cases the disengagement of volatile matter, 

 or of minute air bubbles, — have been considered by several writers 

 as sufficiently accounting for the appearance. Some of the alleged 

 causes here stated, with others which I have considered it unneces- 

 sary to mention, are not likely to be overlooked or to deceive 

 observers of any experience in microscoi)ical research ; and the 

 insufficiency of the most important of those enumerated, may, I 



