312 Professor Tyndall on Germs. 



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 prox- 

 imity 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 me to add a third gas- 

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

 the experiments are conducted. The warmth of this stove played 

 upon one side of the bell-jar : and on 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 dangers incurred in this field of 

 inquiry the author refers to the excellent paper of Dr. Roberts on 

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

 Roberts fills the bulb of an ordinary pipette to about two-thirds 

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

 the pipette he places a plag of dry cotton-wool. He then hermeti- 

 cally seals the neck and dips 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 co(?l. 

 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 pomt- 

 Cotton-wool free from germs is not to be found, and the plug em- 

 ployed by Dr. Roberts 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 certainly a cause sufiicient to detach a germ now and 

 then from the cotton-wool which would fall into the infusion and 

 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 fertiliza- 

 tion being so rare as Dr. Roberts found it to be is a proof of t'^e 

 care with which his experiments were conducted. But he did find 

 cases of fertillization after prolonged exposure to the boiling tem- 

 perature ; and this caused him to come to the conclusion that 

 under certain rare conditions spontaneous generation may occur. 

 He also found that an alkalised hay-infusion was so difticult to 

 sterilise that it was capable of withstanding the boiling tempera- 

 sure for hours without losing its power of generating life. IJie 

 most careful experiments have been made with this infusion, i ■■ 

 Roberts is certainly ( 

 power. But in the p 

 completely sterilise the i 



