88 Royal Society. 



obviously greater, as with blood, milk, turnip, aud potato, the 

 propoi'tion of fertile preparations was considerable, though even 

 with these (except in the case of milk) the barren preparations 

 were in a large majority. 



The experiments seemed clearly to lead to the conclusion that 

 the normal tissues of plants and animals were incapable of breeding 

 Bacteria and Torulce except under the stimulus of extraneous 

 infection. 



Section III, On the hearing of the facts adduced in the preceding 

 sections on the origin of Bacteria and Torulae, and on the real expla- 

 nation of some of the alleged cases of Ahiogenesis. — Seeing that organic 

 liquids and mixtures sterilized by heat, and the normal juices and 

 tissues, continued permanently barren under the most favourable 

 couditions of air, moisture, warmth, and light, so long as they were 

 preserved from extraneous contamination, and seeing that the 

 admission of ordinary air or water into contact with them was 

 invariably followed by germination, it was impossible to avoid the 

 conclusion that ordinary air and water contain, in addition to 

 their proper elements, multitudes of particles capable of provoking 

 germination. The exact nature of these particles may be a 

 matter of dispute, but the reality of their existence is not doubt- 

 ful ; nor is it doubtful that the ordinary and common development 

 of Bacteria and Toridce is directly due to their agency. 



The greatest difficulty hitherto encountered to the general accept- 

 ance of the panspermic theory has been the appearance of Bacteria 

 (without the possibility of fresh infection) in certain liquids which 

 have been exposed for a considerable time to a boiling heat. Only 

 two explanations of this fact seem possible — either germs preexist- 

 ing in them have survived the heat, or the organisms have arisen 

 in them abiogenetically. These alternatives were subjected to two 

 series of test experiments. In the first series it was proved directly 

 that there exist in ordinary air and water particles which preserve 

 their germinal activity after being boiled for five minutes in pre- 

 viously sterilized liquids. The second series of experiments showed 

 that, in the extraordinary increase of resistance to sterilization by 

 heat exhibited by alkaliuized hay-infusion, the action of the alkali is 

 to heighten the surviving power of preexisting germs, and not to 

 exalt the abiogenic aptitude of the infusion itself. 



The issue of the whole inquiry has been to fully confirm the 

 main propositions of the panspermic theory, and to establish the 

 conclusion that Bacteria and Torulce, when they do not proceed 

 from visible parents like themselves, originate from invisible germs 

 floating in the surrounding aerial and aqueous media. 



Nevertheless the author is unable to withstand the impression 

 that this general and common mode of origin is possibly supple- 

 mented, under rare conditions, by another and an abiogenetic mode 

 of origin. The facts on which this impression rests are com- 

 paratively few. They consist in certain instances of greatly 

 retarded germination of Bacteria in liquids which had been exposed 

 to a boiling heat, and in two very remarkable instances of the 



