304 



NATURE 



{August 1 6, 1877 



ligations by most competent inquirers have followed one another 

 in quick succession, from a review of which we cannot but arrive 

 at a conclusion adverse to the theory of heterogenesis, viz., that 

 no development of organisms, even of the most simple kind, has 

 been satisfactorily observed to occur in circumstances which 

 entirely excluded the possibility of their being descended from 

 germs, or equivalent formative particles, belonging to pre-exist- 

 ing bodies of a similar kind. I can do no more now than name 

 the authors of the most conclusive experiments on this subject, 

 which I do nearly in the order of the publication of their re- 

 searches, as those of Mr. W. N. Hartley in 1S72, Messrs. Pode 

 and Ray Lankester in 1S73, Dr. Burdon Sanderson in that and 

 the following years, Dr. 'W. Roberts in 1S74, Prof Lister in 

 1 87 5, and most recently of Prof Tyndall, Prof. Cohn, and of 

 Messrs. Dallinger and Drysdale.' 



But, admitting that the evidence from direct experiment is 

 such as entirely to shut us out from entertaining the view that 

 spontaneous generation occurs in the present condition of the 

 eaith, we are not relieved from the difficulty of explaining how 

 living organisms or their germs first made their appearance; nor 

 are we debarred from attempting to form hypotheses as to how 

 this may have taken place. First, upon the theory of evolution, 

 which, strictly carried out, supposes the more complex organisms 

 to be derived from the more simple, it might be held that the 

 condilicns affecting the combination of the primary elements of 

 matter into organic forms may at one time have been different 

 from those which now prevail ; and that, under those different 

 conditions, abiogenesis may have been possible, and may have 

 operated to lay the foundations of organic life in the simpler 

 forms in which it at first appeared — a state of things which can 

 only be vaguely surmised, but in regard to which no exact infor- 

 mation can be obtained. Or, secondly, evading the difficulty of 

 strict ci'smical evolution, we might suppose that vital conditions 

 may have been coeval with the first existence of physical and 

 chemical properties in the rest of natural bodies. But this hypo- 

 thesis would be exposed to the objection that, according to the 

 cosmical view generally held by jihysicists, the whole materials 

 composing the earth have originally been subject to incandescent 

 heat. Nor is the difficulty abolished, but only removed to a more 

 remote period by the supposition of the transport of germs from 

 another planet or their intioduction by means of meteorites or 

 mtteoiic dust ; for, besides the objection, arising from the cir- 

 cumstance that these bodies must have been subjected to a very 

 high temperature, we should still have everything to learn as to 

 the way in which the germs arose in the far distant regions of 

 space from which they have been conveyed. 



The incompleteness of the geological record leaves us in the 

 dark as to the time at which the first dawnings of life appeared 

 in the lower strata of the earth's surface. The most recent 

 researches tend to carry the origin of life back to a much earlier 

 period than was at one time believed, and if the famous Eozooii 

 be admitted as evidence, even into that of the Laurentian strata. 

 But even if doubts should prevail with regard to the presence of 

 definite organised forms in the older sedimentary strata, the 

 occurrence in them of carbon in the form of graphite in large 

 quantities makes the previous existence of living organisms at 

 least possible, and it may be that the complete metamorphosis 

 which these rocks have undergone has entirely removed all 

 definite traces of organisation. 



Nor have we the means from geological data of determining 

 whether the beings of the vegetable or of the animal kingdom 

 first made their appearance. If we adopt the view which has 

 for some time been entertained by physiologists that animals are 



* I may refer to Dr. Eastiaii's paper in Nature of June 30, 1870, and to 

 Iris two works, "Ttie Origin of tfie Lowest Organisms," and "The 

 Beginnings of Life." Mr. Hartley's researcfies, wliicll were commenced in 

 1865, are descrilDed in a paper printed in tire ProcecitH^s of tfre Royal 

 Society for 1872, and in fiis " Lectnres on Air," 2iid edition, 1S76, where an 

 interesting account of the whole subject will be found. The experiments of 

 Mr. Pode, of Oxford, and I'r.,f. Ray Lanftester are described iir a paper on 

 the ''Development of Bacteria in Organic Infusions" in the Roy. Soc. 

 Proc. for 1873, p. 349. Dr. Burdon Sanderson's researches are contained 

 in the Rep rts of the Medical OfHcer of the Privy Council, and in various 

 papers in NATtnjE : Dr. W. Roberts's paper is printed in the Transact'ous 

 of the Royal Sciety for 1874, vol. clxiv. p. 457. Prof. Lister's "Contri- 

 bution to the Germ Theory of Putrefaction and other Fermentative 

 Changes," ^c. , is contained in the Transactions of the Royal Society of 

 Edinburgh for 1875, p. 313, and is also given in Natukk. l^rof. Tyndall's 

 researches are described in his papers in the Protwditigs of the Ivoyal 

 Society during ihe last two years. The work of Pri.f. t^'ohn, of Breslau, 

 entitled " Beitriige zur Biologie der Pflanzen," t873-76. contains many 

 memoirs bearing up in this subject, which have been partly published in 

 abstract in \.\tQ Microscopical Journal, in which also will be found, in a 

 series of conlributionr. extending from r873 to ihe present time, the interest- 

 ing observations i.f Mr. W. H. Dallinger and Dr. J. Drysdale. 



entirely dependent, directly or indirectly, on plants for the mate- 

 rial which constitutes their living substance, and that plants, as 

 constructive agents, alone have the power to bring together the 

 elements of lifeless matter from such states as carbonic acid, 

 w.iter, and ammonia, into the condition of the living solid, the 

 inference would be inevitable, at least for the great majority of 

 the animal creation, that they must have been preceded by 

 plants. But pakoontology is as yet silent on this interesting 

 question ; and, if we consider the remarkable approach which is 

 made in structure and properties between the lowest and simplest 

 members of the two kingdoms of organic nature, so that at last 

 all distinction between them seems entirely to vanish, and a set 

 of organisms is found which partake equally of animal and vege- 

 table characters, or, rather, exhibit properties v/hich are common 

 to them both, we shall hesitate to postulate confidently for the 

 primitive antecedence of vegetable life, although, perhaps, in 

 later epochs the pre-existence of vegetables may be looked upon 

 as necessary to the life of more developed animal organisms. 



The reflection forces itself upon us that we are just as ignorant 

 of the mode of first origin of all the compounds of the inorganic 

 elements as we are of that of living matter ; and we may there- 

 fore be excused if we suspend all theory and conjecture until we 

 shall be guided to more reliable hypotheses through the plain 

 track of observation and experiment. 



The practical applications of the increased knowledge of 

 the origin of minute animal and vegetable organisms are so 

 numerous that it would occupy a much longer lime than is at 

 my disposal to give any detailed account of them ; but they are 

 of such immense importance in their commercial, social, and 

 sanitary relations that they ought never to be lost sight of. 



It is now proved beyond doubt that the origin of putrefaction 

 and fermentation is dependent on tlie presence in the substances 

 which are the seat of change in these processes, or in the sur- 

 rounding air, of the germs of minute orgmisms of an animal 

 or vegetable nature, and that the maintenance of the chemical 

 changes in which these processes mainly consist is coincident 

 with and casually (if not essentially) dependent upon the growth 

 and multiplication of these organisms. 



Prof. Lister had the merit of being the first to apply the germ- 

 theory of putrefaction to explain the formation of putrid matters 

 in the living body ; and he has founded on this theory the now 

 well-known antiseptic treatment of wounds, the importance of 

 which it would be difficult to over-estimate. 



The success or failure of plans for the preservation of meat 

 and other articles of food without question depends on the 

 possibility of the complete exclusion of the germs which are the 

 cause of putrefaction and fermentation ; and their management 

 must therefore be founded on the mo^t accurate knowledge of 

 these organisms, and the circumstances influencing the 

 persistence of their vitality and the vigour of their growth. 



The theory of biogenesis has also lately been the guide in the 

 investigation of the causes of various forms of disease, both in 

 the lower animals and in man, with the result of showing that 

 in many of them the infective substance consists in all probability 

 of germs of minute animal or vegetable organisms. 



There is very great probability, indeed, that all the zymotic 

 diseases, by which we understand the various forms of fevers, 

 have a similar origin. As has been well remarked by Baxter in 

 an able paper on " The Action of Disinfectants," the analogic; 

 of action of contagia are similar to those of septic organisms, 

 not to processes simply of oxidation or deoxid.ttion. These 

 organisms, studied in suitable fluids, multiply indefinitely when 

 introduced in all but infinitesimal proportions. Tlius they ate, 

 as near as we can perceive, the very essence of contagia.' 



Leaving, however, these and many other general questions 

 regarding the origin of the lowest forms of animal and vegetable 

 life, let us now turn our attention to the mode of development 

 of a new being i)i those belonging to the higher groups. The 

 general nature of the formative process, in all instances where 

 fertilised germs are produced, will be best understood by a short 

 sketch of the phenomena ascertained to occur in different kinds 

 of plants. 



In the higher or phanerogamic plants it is generally well 

 known that the combination of two parts of the flower is neces- 

 sary to the production of a seed containing the embryo or young 

 plant. Beginning with the discoveiy of the pollen tubes by 

 Amici in 1823, the careful and minute investigations of a long 



' For the most interesting information on this subject, I cannot do belter 

 than refer to the very aljle reports by Dr. Burdon Sanderson in lire 

 "Reports of the Medical I ttlicer of the Privy Council," 1S73, 1874. and 



