132 SPONTANEOUS GENERATION. 



conclusively demonstrated by Messrs. Dallinger and Drysdale, in their 

 accounts of the life-history of various species of monads, contributed chiefly 

 to the 'Monthly Microscopical Journal' during the years 1873 to 1875, and 

 as described hereafter, systematically, under the specific headings of Monas 

 Dallingeri, Cercomonas typica, and Heteromita rostrata and uncinata. As 

 there recorded, the spores or germs of these animalcules, when first released 

 by the rupture of their enclosing cyst,, are of such extreme minuteness 

 as to defy individual resolution with a 3 Vinch objective and associated 

 magnifying power of no less than 15,000 diameters, appearing in the 

 aggregate under such conditions as a faintly granular fluid, having a re- 

 fractive index scarcely distinguishable from the surrounding water. As 

 germination and development progress, each individual spore, however, 

 passes within the range of vision, and by degrees assumes the determinate 

 size, form, and characteristics of the parent organism. The record of 

 these reproductive phenomena of the monads in question was brought 

 forward at the time simply as a newly discovered and interesting chapter 

 in their life-history. Later on, however, Mr. Dallinger published in the 

 'Monthly Microscopical Journal' for December 1876, the results of his 

 further investigations of these minute organisms, in which, through corre- 

 lating his own discoveries with those of Professor Tyndall, he obtained 

 some most important results. 



Drying up the residual portion of a maceration or infusion containing a 

 certain known form of monad, he had already shown that the light, porous, 

 papier-mache-like substance resulting from such desiccation might be 

 saved, like the seeds of a plant, and used for propagating the species at 

 will in any suitable sterilized putrescible fluid. Working on this basis, 

 an infusion of haddock's head, containing in abundance the so-called 

 " Springing Monad" (Heteromita rostrate?) and the Calycine Monad (Tetra- 

 mitus rostratus) in the spore-producing stage, was gradually evaporated, 

 then raised to a temperature of 150 Fahr., or 10 above that required to 

 kill the adult form, and so reduced to a porous and highly friable condition. 

 A small portion of this dried material, reduced to powder, was now diffused 

 in an experimental chamber like those employed by Professor Tyndall, 

 and the condensed beam of an oxyhydrogen lime-light being transmitted 

 through the windows, its path within the chamber was more brilliantly 

 marked than on the outride, indicating the preponderating existence therein 

 of the spore-containing or germinal dust. This was now allowed to settle 

 for a space of four hours and a half, when the lime-light still demonstrated, 

 though in a less marked manner, the presence of the suspended dust. Ten 

 small glass dishes, each partially filled with a sterilized fluid, were then 

 introduced into the chamber, four of them being covered with projecting 

 glass lids, mechanically movable, without opening the door of the chamber, 

 and smeared with glycerine, to prevent the disturbance of any previously 

 settled germs. At. the end of twenty-four hours the lids were removed 

 from the four covered vessels, and the whole now left undisturbed for 



