59 6 THE POPULAR SCIENCE MONTHLY. 



substitute, for the adventurous conclusion that an organic infusion is 

 barren at one place and spontaneously generative at another, the more 

 rational and obvious one that the air of the two localities which has 

 had access to the infusion is infective in different degrees? 



As regards workmanship, moreover, he will not fail to bear in 

 mind that fruitfulness may be due to errors of manipulation, while 

 barrenness involves the presumption of correct experiment. It is only 

 the careful worker that can secure the latter, while it is open to every 

 novice to obtain the former. Barrenness is the result at which the 

 conscientious experimenter, whatever his theoretic convictions may 

 be, ought to aim, omitting no pains to secure it, and resorting, only 

 when there is no escape from it, to the conclusion that the life observed 

 comes from no source which correct experiment could neutralize or 

 avoid. Let us again take a definite case. Supposing my colleague to 

 operate with the same apparent care on 100 infusions or rather on 

 100 samples of the same infusion and that 50 of them prove fruitful 

 and 50 barren. Are we to say that the evidence for and against 

 heterogeny is equally balanced? There are some who would not only 

 say this, but who would treasure up the 50 fruitful flasks, as "posi- 

 tive results, and lower the evidential value of the 50 barren flasks by 

 labeling them " negative '' results. This, as shown by Dr. William 

 Roberts, is an exact inversion of the true order of the terms positive 

 and negative. 1 Not such, I trust, would be the course pursued by my 

 friend. As regards the 50 fruitful flasks he would, I doubt not, 

 repeat the experiment with redoubled care and scrutiny, and, not by 

 one repetition only, but by many, assure himself that he had not fallen 

 into error. Such faithful scrutiny fully carried out would infallibly 

 lead him to the conclusion that here, as in all other cases, the evidence 

 in favor of spontaneous generation crumbles in the grasp of the com- 

 petent inquirer. 



The botanist knows that different seeds possess different powers 

 of resistance to heat. 2 Some are killed by a momentary exposure to 

 the boiling temperature, while others withstand it for several hours. 

 Most of our ordinary seeds are rapidly killed, while Pouchet made 

 known to the Paris Academy of Sciences, in 1866, that certain seeds, 

 which had been transported in fleeces of wool from Brazil, germinated 

 after four hours' boiling. The germs of the air vary as much among 

 themselves as the seeds of the botanist. In some localities the diffused 

 germs are so tender that boiling for five minutes, or even less, would 

 be sure to destroy them all; in other localities the diffused germs are 



1 See . his truly philosophical remarks on this head in the British Medical Journal, 

 18*76, p. 282. 



2 I am indebted to Dr. Thistleton Dyer for various illustrations of such differences. It 

 is, however, surprising that a subject of such high scientific importance should not have 

 been more thoroughly explored. Here the scoundrels who deal in killed seeds might be 

 able to add to our knowledge. 



