SPONTA NEO US GENERA TIOK 



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experiment may be as hard to perform as it is 

 easy to enunciate. If we consider how much is 

 involved in the direction to take dead matter, 

 how much again in the requirement of absolute 

 isolation, and how much more in the selection of 

 conditions for life-evolution and the determina- 

 tion of the presence or absence of life at the 

 close of the process, we shall begin to understand 

 why so long a time and so much honest labor 

 have been consumed without arriving at a final 

 verdict. But everything points to a speedy con- 

 clusion. By a long course of patient work, con- 

 trolled by eager criticism, the methods of pro- 

 cedure have been gradually perfected and simpli- 

 fied, the opposing ranks have closed, as it would 

 seem, for their decisive struggle, the champions 

 on either side have pressed to the front, and 

 we may reasonably hope before long to see the 

 final upshot of a controversy as old as scientific 

 thought. At such an epoch it may not be unin- 

 teresting to glance at the salient points of the 

 accumulated evidence, perhaps even to hazard a 

 cautious forecast of the impending result. 



In order to comprehend the positions of con- 

 tending forces, it is always essential thoroughly 

 to familiarize ourselves with the battle-ground 

 which they occupy ; and a somewhat closer sur- 

 vey of what we have termed the crucial experi- 

 ment will be found not less essential to any in- 

 telligent appreciation of the position of this con- 

 troversy. And first, what do we mean by dead 

 matter? How is it possible to predicate with 

 certainty the absence of life from anything on the 

 face of the earth ? The microscope has taught 

 us that life in some shape or other abounds in al- 

 most everything about us. Either in active mo- 

 bile vitality, 01 in the suspended animation of 

 germinal existence, life teems in the soil we tread 

 upon, in the water we drink, and, as some say, 

 with equal abundance in the air we breathe. 

 What worlds may exist as far beyond the range 

 of microscopic vision as this surpasses the sphere 

 of ordinary eyesight, no one can do more than 

 guess. How, then, is the first requirement of our 

 experiment to be satisfied? How is the pre- 

 scribed specimen of dead matter to be got ? This 

 is the primary difficulty which investigators of 

 this subject have had to grapple with. Happily 

 it is not insurmountable. It is as certain as any 

 fact in the whole range of science, that all living 

 things and all living germs may be destroyed by 

 the agency of heat. How much heat is needed to 

 effect the destruction of life is still in question, 

 but no one doubts that matter may be made ab- 

 solutely dead by subjecting it to the influence of 



! a sufficiently high temperature. The next condi- 

 tion — perfect isolation from surrounding life, 

 whether active or germinal — has given more 

 trouble, but can now be readily satisfied. All 

 are agreed that no living germ can pass through 

 a sound plate of glass; and a certain — perhaps 

 in practice the only quite certain — method of 

 isolation is to inclose the heated dead matter 

 within a glass vessel hermetically sealed. Other 

 less perfect means have been tried with various 

 degrees of success. Many experimenters have 

 found that the simple expedient of stuffing the 

 narrow neck of a glass vessel with a plug of cot- 

 ton-wool generally suffices to exclude the passage 

 of living germs. Another method sometimes 

 adopted is, to use for the experiment a flask with 

 a long neck, so arranged that a portion of it can 

 be kept at a high temperature, so as to burn out 

 from the passing air every particle of living mat- 

 ter which it may contain. A third expedient, 

 simpler than either of these, is to bend the open 

 neck of the experimental flask alternately upward 

 and downward, so as to form in each bend a re- 

 ceptacle into which the dust, dead or living, of the 

 air will fall ; and it has been said that this method 

 may be relied on as surely protecting the interior 

 of the flask from the approach of living germs, 

 provided the subsidence is not interfered with 

 by currents of air of too great vigor. Yet an- 

 other method is to seal the open orifice of the 

 flask by cementing over it a plate of earthenware, 

 porous enough to admit air where that is desired, 

 but of a texture so close as to bar the passage of 

 the minutest germ. 



All of these methods have been proved again 

 and again to be more or less efficacious, but the 

 only one the success of which can be predicated 

 with absolute certainty is that which we first 

 mentioned, though the last no doubt deserves to 

 be trusted when practised with adequate care. 

 When a glass vessel is hermetically closed we are 

 able to say that its contents are isolated from 

 everything outside which cannot pass through a 

 film of glass. This barrier, it is known, suffices 

 to stop the minute molecules of gas or vapor; 

 and it is beyond doubt that it must exclude all 

 grosser particles, including any living germs which 

 may be supposed to be floating in the air. It was by 

 adopting this process that Spallanzani in the last 

 century turned the tide of opinion against Need- 

 ham, whose results in support of spontaneous 

 generation had been obtained by using a much 

 clumsier method of excluding contamination ; and 

 it is not a little remarkable that after the superi- 

 ority of this treatment had been so signally estab- 



