128 



NA TURE 



{June 14, 1877 



been previously familiar to me, and in the sterilization of 

 which I had never experienced any difficulty. Fish, flesh, 

 and vegetables were re-subjected to trial. Though the 

 precautions taken to avoid contamination were far more 

 stringent than those observed in my first inquiry, and 

 though the interval of boiling was sometimes tripled in 

 duration, these infusions, in almost every instance, broke 

 down. Spontaneously purified air, filtered air, and cal- 

 cined air, — calcined, 1 may add, v/ith far greater severity 

 than was found necessary a year previously, — failed, in 

 almost all cases, to protect the infusions from putrefaction. 



I had the most implicit confidence in the correctness of 

 my earlier experiments ; indeed, incorrectness would have 

 led to consequences exactly opposite to those arrived at. 

 Errors of manipulation would have filled my tubes and 

 flasks with organisms instead of leaving them transparent 

 and void of life. By the unsuccessful experinvents above 

 referred to a clear issue was therefore raised : Either the 

 infusions of fish, flesh, and vegetable had become en- 

 dowed in 1876 with an inherent generative energy which 

 they did not possess in 1875, ""^ some new contagium ex- 

 ternal to the infusions, and of a far more obstinate cha- 

 racter than that of 1875, had been brought to bear upon 

 them. The scientific mind will not halt in its decision 

 between these two alternatives. 



For my own part the gradual but irresistible interaction 

 of thought and experiment rendered it at first probable, 

 and at last certain that the atmosphere in which I worked 

 had become so virulently infective as to render utterly 

 impotent precautions against contamination, and modes 

 of sterilization, which had been found uniformly successful 

 in a less contagious air. I therefore removed from the 

 laboratory, first to the top, and afterwards to the base- 

 ment of the Royal Institution, but found that even here, 

 in a multitude of cases, failure was predominant, if not 

 uniform. This hard discipline of defeat was needed to 

 render me acquainted with all the possibilities of infection 

 involved in the construction of my chambers and the 

 treatment of my infusions. 



I finally resolved to break away from the Royal Insti- 

 tution, and to seek at a distance from it a less infective 

 atmosphere. In Kew Gardens, thanks to our President, 

 the requisite conditions were found. I chose for exposure 

 in the Jodiell laboratory the special infusions which had 

 proved most intractable in the laboratory of the Royal 

 Institution. The result was that liquids which in Albe- 

 marle Street resisted two hundred minutes boiling, be- 

 coming fruitful afterwards, were utterly sterilised by five 

 minutes' boiling at Kew. 



A second clear issue is thus placed before the Royal 

 Society : — Either the infusions had lost in Kew Gardens 

 an inherent generative energy which they possessed in 

 our laboratory, or the remarkable instances of life deve- 

 lopment, after long-continutd boiling, observed in the 

 laboratory are to be referred to the contagium of its air. 



With a view to making nearer home experiments similar 

 to those executed at Kew, I had a shed erected on the 

 roof of the Royal Institution. In this shed infusions were 

 prepared and introduced into new chambers of burnished 

 tin, which had never been permitted to enter our labora- 

 tory. After their introduction the liquids were boiled for 

 five minutes in an oil-bath. 



The first experiment in this shed resulted in complete 

 failure, the air of the shed proving to be sensibly as in- 

 fective as the air of the laboratory. 



Either of two causes, or both of them combined, might, 

 from my point of view, have produced this result. First, 

 a flue from the laboratory was in free communication with 

 the atmosphere not far from the shed ; secondly, and this 

 was the real cause of the infection, my assistants in 

 preparing the infusions, had freely passed from the 

 laboratory to the shed. They had thus carried the con- 

 tagium by a mode of transfer known to every physician. 



The infected shed was disinfected ; the infusions were 



again prepared, and care was taken, by the use of proper 

 clothes, to avoid the former causes of contamination. 

 The result was similar to that obtained at Kew, viz., 

 organic liquids which in the laboratory withstood two 

 hundred minutes' boiling, were rendered permanently 

 barren by five minutes' boiling in the shed. 



A third clear issue is thus placed before us, which 

 I should hardly think of formulating before the Royal 

 Society, were it not for the incredible confusion which 

 apparently besets this subject in the public mind. A rod 

 thirty feet in length would stretch from the infusions in 

 the shed to the same infusions in the laboratory. At one 

 end of this rod the infusions were sterilized by five 

 minutes' boiling, at the other end they withstood two 

 hundred minutes' boiling. As before, the choice rests 

 between two inferences: — Either we infer that at one end 

 of the rod animal and vegetable infusions possess a 

 generative power, which at the other end they do not 

 possess ; or we are driven to the conclusion that at the 

 one end of the rod we have infected, and at the other end 

 disinfected air. 



The second inference is that which will be accepted by 

 the scientific mind. To what, then, is the inferred dif- 

 ference at the two ends of the rod to be ascribed? In 

 one obvious particular the laboratory this year differed 

 from that in which my first experiments were made. On 

 its floor were various bundles of old and desiccated hay, 

 from which, when stirred, clouds of fine dust ascended 

 into the atmosphere. This dust proved to be both fruitful 

 and in the highest degree resistant. Prior to the intro- 

 duction of the hay which produced the dust, no difficulty 

 as regards sterilization had ever been experienced ; sub- 

 sequent to its introduction my difficulties and defeats 

 began. 



In these and numerous other experiments a method 

 was followed which had been substantially employed by 

 Spallanzani and Needham ; and more recently by Wyman 

 and Roberts, the method having been greatly refined by 

 the philosopher last named. The flasks containing the 

 infusions were only partially filled, the portions unoccupied 

 by the liquids being taken up with ordinary unfiltered air. 

 Now as regards the death-point of contagia, we know 

 that in air it is higher than in water, the self-same 

 temperature being fatal in the latter and sensibly harm- 

 less in the former. Hence my doubt whether, in my 

 recent experiments, the resistance of the contagium did 

 not arise from the fact that it was surrounded, not by 

 water but by air. 



I changed the method, and made a long series of 

 experiments with filtered air. They were almost as un- 

 successful as those made with ordinary air. 



One source of discomfort clung persistently to my mind 

 throughout these e.xperiments. I was by no means cer- 

 tain that the observed development of life was not due to 

 germs entangled in the film of liquid adherent to the 

 necks and higher interior surfaces of the bulbs. This film 

 might have dried, and its genns, surrounded by air and 

 vapour, instead of by water, might on this account have 

 been able to withstand an ordeal to which they would 

 have succumbed if submerged. 



A plan was, therefore, resorted to by which the infu- 

 sions were driven by atmospheric pressure through lateral 

 channels issuing from the centres of the bulbs. As before, 

 each bulb was filled with one-third of an atmosphere of 

 filtered air, and afterwards heated nearly to redness. 

 When fully charged, the infusion rose higher than the 

 central orifice, and no portion of the internal surface was 

 wetted save that against which the liquid permanently 

 rested. The lateral channel was then closed with a 

 lamp without] an instant's contact being permitted to 

 occur between any part of the infusion and the external 

 air. It was thus rendered absolutely certain that the 

 contagia exposed subsequently to the action of heat were 

 to be sought, neither in the superjacent air nor on the in- 



