70 Royal Society. 



fche bell-jar was imbedded. For three weeks the infusions had re- 

 mained perfectly clear. At the end of this time, with a view of 

 renewing the air of the jar, it was exhausted, and refilled by fresh 

 air which had parsed through a plug of cotton-wool. As the air 

 entered, two small spots of Penicillium, resting on the liquid 

 which had boiled over, attracted attention. It was at once 

 remarked that the experiment was a dangerous one, as the enter- 

 ing air would probably detach some of the spores of the Penicillium 

 and diffuse them in the bell-jar. This was therefore filled very 

 slowly, so as to render the disturbance a minimum. Next day, 

 however, a tuft of mycelium was observed at the bottom of one 

 of the three tubes, namely that containing the hay-infusion. It 

 has by this time grown so as to fill a large portion of the tube. For 

 nearly a month longer the two tubes containing the turnip- and 

 mutton-infusions maintained their transparency unimpaired. Late 

 in December the mutton-infusion, which was in dangerous proxi- 

 mity to the outer mould, showed a tuft upon its surface. The 

 beef-infusion continued bright and clear for nearly a fortnight 

 longer. The recent cold weather caused the author to add a third 

 gas-stove to the two which had previously warmed the room in 

 which the experiments are conducted. The warmth played upon 

 one side of the bell-jar, causing currents within it ; and the day 

 after the lighting of the stove, the beef-infusion gave birth to 

 a tuft of mycelium. In this case the small spots of Penicillium 

 might have readily escaped attention; and had they done so 

 we should have had three cases of "spontaneous generation'' far 

 more striking than many that have been adduced. 



In further illustration of the danger incurred in this field of in- 

 quiry, the author refers to the excellent paper of Dr. Eoberts on 

 Biogenesis, in the Philosophical Transactions for 1874. Dr. Eoberts 

 fills the bulb of an ordinary pipette up to about two thirds of 

 its capacity with the infusion to be examined. In the neck of the 

 pipette he places a plug of dry cotton-wool. He then hermetically 

 seals the neck, and clips the bulb into boiling water or hot oil, 

 where he permits it to remain for the requisite time. Here we 

 have no disturbance from ebullition and no loss by evaporation. 

 The bulb is removed from the hot water and permitted to cool. 

 The sealed end of the neck is then filed off, the cotton- wool alone, 

 interposing between the infusion and the atmosphere. 



The arrangement is beautiful, but it has one weak point. Cotton- 

 wool free from germs is not to be found, and the plug employed 

 by Dr. Eoberts infallibly contained them. In the gentle movement 

 of the air to and fro, as the temperature changed, or by any shock, 

 jar, or motion to which the pipette might be subjected, we have cer- 

 tainly a cause sufficient to detach a germ now and then from the 

 cotton-wool which, falling into the infusion, would produce its 

 effect. Probably also condensation occurred at times in the neck 

 of the pipette, the water of condensation carrying back from the 

 cotton-wool the seeds of life. The fact of fertilization being so rare 

 as Dr. Eoberts found it to be, is a proof of the care with which his 



