SPONTANEOUS GENERATION. 299 



The Dimensions of Crystalline Germs Compar- 

 able to those of Microbes. — We may dilute the solid 

 salol with inert powder — lactin, for example — dilute 

 the first mixture with a second, the second with a 

 third, and so on; then, throwing into the solution of 

 surfused salol a tenth of a milligram from one of 

 these various mixtures, we find that the production of 

 crystals will not take place if the fragment thrown in 

 weighs less than a millionth of a milligram, or 

 measures less than ten thousandths of a millimetre 

 in length. It would seem, then, that these are the 

 dimensions of the crystalline particle or crystallo- 

 graphic molecule of salol. In the same way Ostwald 

 satisfied himself that the crystalline germ of hypo- 

 sulphite of soda weighs about a thousand-millionth of 

 a milligram, and measures a thousandth of a milli- 

 metre ; that of chlorate of soda weighs a ten-millionth 

 of a milligram. These dimensions are entirely com- 

 parable with those of microbes. 



All these phenomena have been studied with a 

 detail into which it is impossible to enter here, and 

 which clearly shows more and more intimate analogies 

 between the formation of crystals and the generation 

 of micro-organisms. 



Extension and Propagation of Crystallization. 

 Optimum Temperature of Incubation. — Crystallization 

 which has commenced around a germ is propagated 

 more or less rapidly, and ends by invading the whole 

 of the liquor. 



The rapidity of this movement of extension depends 

 upon the conditions of the medium, especially upon 

 its temperature. This is shown very well by 

 Tammann's experiments with betol. This body, 

 the salicylic ester of naphthol, fuses at 96° C. If it 



