166 
PROFESSOR TYNDALL ON THE DEPORTMENT AND VITAL 
respite, for a day or two subsequently it fell into the condition of its neighbours. On 
the 30th of November both turnip- and parsnep-infusions were turbid throughout, and 
laden at the surface with thick fatty scum. The cucumber was also heavily laden 
with scum, which sent long streamer-like filaments into the subjacent liquid. The 
beetroot agreed with the others in becoming turbid, but differed from them in remaining 
free from scum. In no case last year did turnip-infusion show the deportment here 
described. Knowing, then, from multiplied experiments, that turnip possessed no 
inherent power of life-development, I was forced to refer its present behaviour, and 
with it the behaviour of cucumber, beetroot, and parsnep, to infection from without. 
I once more tried removal to a distant room, with the added precaution of not 
only introducing the infusions 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It had been noticed that when the test-tubes were withdrawn from the oil-bath, and 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 different 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 1 The case of my two trays placed one above the other last year * 
suggested itself to my memory. In point of life-development it was then found that 
the lower tray was always in advance of the upper one. As pointed out at the time, 
the absence of agitation which permitted the germs to sink into its tubes was the 
cause of the quicker contamination of the lower tray. N o other cause appeared to me 
assignable in the present instance. By some means or other germs had insinuated 
themselves into my closed chamber, where the tranquillity of the air permitted them 
to sink into the infusion, and thus produce effects in advance of those produced by the 
unquiet air outside. So I reasoned. 
But how could the germs get into the chamber 1 I could fix at the moment only 
upon one way. The weather had changed from warm to cold and from cold to warm. 
This genial outside temperature sometimes caused the air surrounding the infusions 
to rise to upwards of 90° Fahr., and we had often to work in this heat. To 
* Phil. Trans, vol. clxyi. p. 68. 
