VITALITY OF PUTEEFACTIVE ORGANISMS. 163 



I once more tried removal to a distant room, with 

 the added precaution of not only introducing the infu- 

 sions into the chambers upstairs, but of boiling them 

 there. It had been noticed that when the test-tubes 

 were withdrawn from the oil-bath, and the discharge 

 of steam into the chambers ceased, a somewhat violent 

 entrance of the air into the cooling chamber was the 

 consequence. To sift such air of its germs, both the 

 funnel of the pipette and the open ends of the bent 

 tubes were carefully stopped with cotton-wool. The 

 wool was never removed from the funnel, and it was 

 not removed from the bent tubes until the chamber had 

 thoroughly cooled. The same vegetables were operated 

 on, viz. cucumber, beetroot, turnip, and parsnep. On 

 the 25th of November four chambers were charged with 

 the infusions. On the 30th they were one and all covered 

 with a layer of deeply pitted and corrugated fatty 

 scum. Thus far, then, I was defeated in my efforts to 

 escape contamination. 



During these experiments a fact was observed which 

 repeated itself afterwards in other instances. Samples 

 of the diflferent infusions were always exposed to the 

 common air beside their respective chambers, and in 

 general these outside samples became turbid and covered 

 with scum a day or so before the interior tubes gave 

 notice of breaking down ; but here, in the case of the 

 turnip, the outside tube continued pellucid and free 

 from life for some time after the inside ones had become 

 turbid with organisms. How could this be ? The case 

 of my two trays placed one above the other last year ' 

 suggested itself to my memory. In regard to life-de- 

 velopment it was then found that the lower tray was 

 always in advance of the upper one. As pointed out 



1 Phil. Trans., vol. clxvi. p. 68. 



