Dr. W. Roberts on Biogenesis, 87 



origin of Bacteria aud toruloid vegetations. The inquiry is divided 

 into three sections. 



Section I. On the sterilization hy heat of organic, lufuds and 

 mixtures. — When beef-tea or a decoction of turnip is boiled for a 

 few minutes and afterwards preserved from extraneous contami- 

 nation, it passes into a state of " permanent sterility." 



This state is characterized by loss of power to originate organisms 

 with conservation of the power of nourishing and promoting the 

 growth of organisms. 



All organic liquids and mixtures seem capable of being brought 

 to this state by exposure to the heat of 212° F. ; but the length of 

 time during which exposure to this heat is necessary to induce 

 sterilization varies greatly according to the nature of the materials. 

 Ordinary infusions and decoctions were sterilized by boiling for 

 five or ten minutes ; but milk, chopped green vegetables in water, 

 pieces of boiled egg in water, and other mixtures were not 

 sterilized unless the heat was continued for twenty to forty 

 minutes. Hay-infusion was sterilized, like other infusions, by 

 boiling for a few minutes ; but when the iiafusion was rendered 

 alkaline \vith ammonia or liquor potassse, it was not sterilized 

 except after an exposure to the heat of boiling water for more 

 than an hour. Sometimes it germinated after two hours, and 

 once after three hours of such exposure. 



There appeared to be two factors of equal importance in the 

 induction of sterilization — namely, the degree of heat and the 

 duration of its application. These tvro factors appeared to be 

 mutually compensatory in such fashion that a longer exposure to a 

 lower temperature was equivalent to 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 capahilitg of the nornud tissues and juices to 

 generate Bacteria and Torula) luithout extraneous infection. — The 

 following substances were examined : — egg-albumen, blood, urine, 

 blister-serum, milk, grape-, orange- and tomato-juice, turnip and 

 potato. These substances were conveyed into pi-eviously 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 tem- 

 perature ranging from 60° to 90° ¥., 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 perfection, as with urine, blister- 

 serum, orange-, grape-, aud tomato-juice (34 experiments), the 

 preparations, all save one, remained barren ; but when the risks 

 of extraneous infection were (from the mechanical dilUculties) 



