SPONTANEOUS GENERATION. 



119 



which never engendered life unless previously 

 inoculated with breeding bacteria, and never 

 failed to do so when it was so inoculated, the 

 problem would be solved. We should then pos- 

 sess a reagent by which to test the existence of 

 bacterial life, germinal or otherwise, as readily as 

 arsenic or oxalic acid can be detected by the ap- 

 propriate chemical tests. Fortunately there is no 

 difficulty in finding fluids of this quality. There 

 are solutions of chemical salts in which a drop 

 of putrefying fluid will produce rapid and visible 

 multiplication of bacteria, although the test fluid, 

 if left to itself and protected from contamination, 

 will never engender them. Similar test-fluids 

 may be produced by suitable treatment of some 

 organic infusions, among them rather weak solu- 

 tions of turnip and hay. Here, then, the test is 

 furnished, and nothing is simpler than to ascer- 

 tain the temperature which will destroy bacterial 

 life. Take a mass of putrefying liquid in which 

 bacteria are rapidly multiplying. Inoculate the 

 test-fluid with a drop of the mixture — bacteria, 

 germs and all — heat it to the required tempera- 

 ture, and see whether multiplication follows. If 

 it becomes cloudy in a day or two, you are sure 

 that the inoculating drop contained living bacte- 

 ria or their germs, and that the heat applied was 

 short of the death-point in the particular fluid 

 used. If the test-fluid remains clear, it is equally 

 certain that the heat has sufficed to kill all life, 

 or, at any rate, all reproductive life, within it. 

 The investigation was pursued in this way by 

 Dr. Bastian. 1 The results are very remarkable. 

 They show that when the fluid employed, whether 

 a saline solution, an acid turnip, or neutral hay 

 infusion, was heated above 158° Fahr., the bac- 

 teria and germs within it absolutely lost the power 

 of multiplication; while, if heated only to 130°, 

 they always retained vitality. The precise heat 

 which produced sterility in different fluids varied 

 between these limits, but 158° was found to be 

 the maximum temperature which a growing and 

 multiplying swarm of bacteria, with their families 

 and their germs, could in any of these cases 

 survive. 



These experiments have never, so far as we 

 know, been repeated. They cannot, therefore, 

 rank with confirmed investigations ; but of course 

 no germ-theorist who has not gone over the same 

 ground with inconsistent results can be heard to 

 dispute their accuracy. Outside inquirers may 

 legitimately reserve their unqualified acceptance 

 until the work has been repeated, and the conclu- 

 sions confirmed by independent investigators ; but 

 1 " Evolution and the Origin of Life," pp. 79-129. 



in the mean time it must be acknowledged, at 

 least as a prima-facie truth, that in certain turnip 

 and hay infusions, no less than in solutions of 

 mineral salts, a temperature of 54° short of the 

 boiling-point is sufficient to destroy the life of 

 bacteria and any germs of bacteria. 



Coupling this conclusion with the results be- 

 fore discussed of the experiments on boiled and 

 protected fluids, the spontaneous-generation the- 

 ory would follow as a mere matter of logic. 

 If all reproductive life in a putrefying hay or tur- 

 nip infusion is killed by a temperature of 158°, 

 and yet another infusion of the same substances 

 (differing only in strength and in some particulars 

 of treatment) can produce life after being boiled 

 and protected from contamination, that life must 

 have come from something other than germs, or, 

 in other words, must have arisen de novo. Still 

 it is prudent to bear in mind that observations 

 which have remained for a year or two unques- 

 tioned may be disputed and possibly displaced ; 

 and, however irresistible the ad-hominem argu- 

 ments may be against opponents who have not 

 ventured to grapple with these death-point ex- 

 periments, the final verdict of Science will not be 

 given, and ought not to be given, without further 

 confirmation, or until full time has been allowed 

 for some champion of the germ-theory to enter 

 the lists and combat experimental conclusions 

 which, while they stand, are fatal to his creed. 



As has been already indicated, some approach 

 to such a struggle has been recently made. It 

 has taken the form, not indeed of a direct impeach- 

 ment of the specific results last referred to, but 

 still of a definite issue which involves to a certain 

 extent the same question. The challenger in this 

 instance is Pasteur himself, the Achilles of his 

 host. His opponent we need scarcely say is Bas- 

 tian, the acknowledged chief of the opposing fac- 

 tion. And the precise dispute is this : It had 

 long been recognized on both sides that heating, 

 and especially prolonged heating, beyond the 

 boiling - point, had a strong tendency to check 

 subsequent putrefaction ; and the germ-theorists 

 very fairly made a great point of this. It was an 

 obviously natural inference that if an infusion 

 would vivify after exposure to a temperature of 

 100°, and failed to do so if the previous heating 

 were carried up to 105°, 110°, 120°, or 150°, as 

 was found to be the case in various fluids, the 

 positive results obtained with the lower tempera- 

 ture were due to the survival of germs, while the 

 negative results, often brought about by severer 

 heating, showed that in those cases the death- 

 point had been reached. The explanation offered 



