428 THE LIFE OF MATTER. 



The irietastable and lahile zones.- — This fact is general. There is for 

 each snl)stance a set of conditions (temperature, degree of concen- 

 tration, volume of the sohition) in which the cr^'stalline individuals 

 can V)e produced oidy l)y germs or by tiiiation. This is what occurs 

 for betol above the temperature of 30'. The body is th<Mi in what 

 Ostwuld has called a nietastahle zone. There is, however, for the 

 same body another set of circumstances more or less complex, in 

 which its germs appear spontaneously. This is what happens for betol 

 at about the temperature of 10°. These circumstances are those of the 

 lah'de zone or of spontaneous generation. 



Crystah of glycerin. — We may g-o a step further. Let us suppose, 

 as does L. Errera, that we have a liquid that is found in a state of 

 metastable equilil)rium and whose labile equilibrium is yet unknown. 

 This is what actuall}^ occurs for a very widel}" known l:)ody, glycerin. 

 We do not know under what conditions glvcerin crystallizes spon- 

 taneousl3\ If we cool it, it becomes viscous; we can not obtain its 

 crystals in that way. We did not even obtain its crystals in any way 

 before the year 1867. In that year, in a tun sent from Vienna to 

 London during winter, crj^stallized glycerin was found and Crookes 

 showed these crystals to the Chemical Society of London. What cir- 

 cumstances had determined their formation? We were ignorant of 

 them then and are still ignorant of them. It ma}^ be said that this 

 case of spontaneous generation of the crystals of glycerin has not 

 remained isolated. M. Henninger has noted the accidental foi'mation 

 of gl3^cerin cr3^stals in a manufactory^ of St. Denis. 



It may be remarked that this crystalline species appeared, as living 

 species may have done, at a given moment in an environment in which 

 a favorable chance combined the conditions for its production. It is 

 also quite comparable to the creation of a living species; for having 

 once appeared, we have been able to perpetuate it. The crystalline 

 individuals of 1867 have had a posterity. The}" hav^e been sown in 

 glycerin in a state of surfusion and there reproduced themselves. 

 These generations have been sufficiently numerous to spread the species 

 throughout a great part of Europe. M. Hoogewerf showed numerous 

 examples of them filling a great flask to the Dutch naturalists who 

 met at Utrecht in 1891. M. L. Errera presented others in June, 1899, 

 to the Society of Medical and Natural Sciences at Brussels. To-day 

 the great manufactory of Sarg & Co., of Vienna, engages in their pro- 

 duction on a grand scale for industrial pur[)oses. 



We have been al)le to study this crystalline species of glj^cerin and 

 to determine with precision the conditions which permit it to subsist. 

 It has be(>n shown that it does not resist a temperature of 18 , so that 

 if precautions were not taken to preserve it, a single suuuuer would 

 suffice to annihilate all its crystalline individuals that exist on the 

 surface of the globe, and thus extinguish the sp<H-ies. 



