290 Dr. W. Roberts on Biogenesis. [Apr. 16, 



a shorter exposure to a higher temperature. For example, speaking 

 roughly, an exposure for an hour to a heat of 212 F. appeared to be 

 equivalent to an exposure for fifteen minutes to a heat of 228 F. 



SECTION II. On the capability of the normal tissues and juices to generate 

 Bacteria and Torulae without extraneous infection. The following sub- 

 stances were examined : egg-albumen, blood, urine, blister-serum, milk, 

 grape, orange- and tomato-juice, turnip and potato. These substances 

 were conveyed into previously prepared sterilized bulbs and tubes, which 

 were hermetically sealed at one end and plugged with cotton-wool at the 

 other end. When the several steps of the experiment were quickly and 

 dexterously performed, the risks of extraneous contamination, although 

 not altogether avoided, were reduced to small proportions. The bulbs 

 and tubes thus charged were afterwards maintained at a temperature 

 ranging from 60 to 90 F., and were finally examined at periods varying 

 from four to ten weeks. Out of 90 experiments performed in this way, 

 67 preparations remained barren and 23 became fertile. When the ideal 

 conditions of the experiment could be carried out in approximative per- 

 fection, as with urine, blister-serum, orange-, grape-, and tomato-juice 

 (34 experiments), the preparations, all save one, remained barren ; but 

 when the risks of extraneous infection were (from the mechanical dif- 

 ficulties) obviously greater, as with blood, milk, turnip, and potato, the 

 proportion 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 bearing of the facts adduced in the preceding sec- 

 tions on the origin of Bacteria and Torulaa, and on the real explanation of 

 some of the alleged cases of Abiogenesis. Seeing that organic liquids and 

 mixtures sterilized by heat, and the normal juices and tissues, continued 

 permanently barren under the most favourable conditions of air, moisture, 

 warmth, and light, so long as they were preserved from extraneous con- 

 tamination, and seeing that the admission of ordinary air or water into 

 contact with them was invariably followed by germination, it was im- 

 possible to avoid the conclusion that ordinary air and water contain, in 

 addition to their proper elements, multitudes of particles capable of pro- 

 voking germination. The exact nature of these particles may be a 

 matter of dispute, but the reality of their existence is not doubtful ; nor 

 is it doubtful that the ordinary and common development of Bacteria and 

 Torulce is directly due to their agency. 



The greatest difficulty hitherto encountered to the general acceptance 

 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 



