Science

Saved Stories

IF we return again so soon to the Spontaneous Generation controversy, it is for several good reasons. First, the theoretical importance of the question is immense. Second, from the monotony of the experiments, almost all of them being concerned with flasks and degrees of the thermometer, we know by trial how hard it is to keep a distinct “ tally” in one’s head of the number of points each side has recorded in its favor, and how useful a clear summary from time to time may be. And, third, the subject is in so rapid a state of development, that every few months enables one to shape a few more questions, if not conclusions. And in science a wellput question may be as useful as a conclusion.

Referring our readers back to the Atlantic for January and May of this year for an account of the question prior to, and at the publication of, Dr. Bastian’s book, we will only say that at its appearance it was pretty roughly handled by many critics. From the first, Dr. Bastian’s career has been unusually marked in this way. Not only has the Huxleyan hoof left its print upon him, but biologists of a lesser growth have taken pains to treat him with personal contempt. It may be that his early work deserved this, and left a presumption that all he might do would prove to be but rough experiment and rash conclusion. Certainly the brunt of the criticisms was that Dr. Bastian could not be depended on for his facts. Professor Huxley said he should as soon believe a geranium or a gold snuff-box to be generated in an infusion flask as some of the things Dr. Bastian said he had found there. In short, when he said that flasks of turnip infusion, sealed while boiling so that the fluid remained in vacuo, were productive of bacteria, every one denied the fact of production, and not the probability of the boiling heat having destroyed all the germs that may have pre-existed in the flask. They, hardly any one doubted, died far below 100° C. But when Dr. Bardon-Sanderson, whose authority as an experimenter no one seems to doubt, came out in the journal Nature with a communication corroborating in every point what Dr. Bastian had advanced regarding the behavior of turnip infusions, the tactics of the pauspermatists had to change. And the vital question now is one that was formerly supposed settled, namely, To how high a temperature may organic germs be exposed, and yet remain capable of propagation? Whether the theory which Dr. Bastian upholds prove true or false ultimately, it is now certain that he will remain in possession of a most honorable reputation as a persevering, profound, and, in all that regards bacteria at any rate, accurate investigator.

The ultimate decision of the question will, we think, depend on a balance of probabilities. The germs whose existence is to be decided are confessedly invisible by the highest microscopic powers, and any direct assurance that they are excluded or not, or killed or not, is impossible. A crucial test experiment seems also impossible to contrive. And w.e shall have to look about therefore for as extensive a mass of facts as possible, and see which theory, that of germs or that of spontaneous molecular reconstruction, is, on the whole, the simplest and easiest “fit” for them all. Pasteur, taking a single series of data, arranges them so as triumphantly to point to a conclusion in favor of the germs ; Bastian is now able to arrange another set so as to point almost as persuasively to evolution. But neither Pasteur’s nor Bastian’s series leaves an opposite explanation impossible. To take a few examples, Huizinga (in Nature, May, 29, 1873) thinks he has proved the genesis of bacteria without germs in this way: he takes three fluids, composed respectively of a solution of certain salts and peptone, of the same with the addition of glucose, and of the salts, glucose, and urea. Each solution is an excellent nidus for bacteria (i. e. it will swarm with the creatures if a drop of fluid containing them be sown in it), but if three sets of flasks are filled, each set with one of the solutions, boiled ten minutes and closed while boiling with a hot tile cemented by asphalt to the rim of the flask, so that the air which enters as the flask cools may be strained of its dust and germs by the porous clay, all containing the secondnamed fluid will be fertile, while all of the two other sets remain barren. The barrenness of the two other fluids proves, this author thinks, that the boiling heat destroyed all germs within the flask, whilst the tile excluded all new-comers from without. If germs had survived the heat and filtration, they would infallibly have developed in these two niduses. Ergo in the other flasks which were fertile there could have been no germs, for they were subjected to identical physical conditions; and their fertility was then independent of germs. But this reasoning wholly ignores the possibility that germs in one fluid may survive a degree of heat which in another would be fatal to them. Their vital resistance may be not simply a resistance to thermal, but to thermo-chemical death. And the second fluid, being differently composed from the two others, may have let them live for ten minutes even at a boiling heat, so as at last to make it fertile. Or, another possibility still, there may be two kinds of germs present, one most apt for propagation in the second fluid, and capable of resistance to ten minutes’ boiling ; and this may have survived also in the barren fluids, but not developed there, owing to their uncongeniality ; whilst the germs to which they were congenial could not survive the boiling. Either of these possibilities leaves open a door of escape from spontaneous generation. Whether we shall take it depends on their being made, by other evidence, probabilities.

Here is another recent experiment by Dr. Bardon-Sanderson, which he thinks tells against archebiosis : he finds that a turnip and cheese solution which was fertile after exposure to 100° Centigrade was barren if the temperature was carried one or two degrees higher. He supposes that the slight additional rise of heat might easily have made the difference between life and death to germs, but may less easily be supposed to have altered the molecular constitution of the fluid so as to turn it unfit for taking on those molecular reconstructions that archebiosis implies, while it was fit a moment before. Nevertheless, the latter alternative is possible, and we may adopt it if we can make it on other grounds seem probable. And the same balance of probabilities comes in when Dr. Bardon-Sanderson then inoculates the barren fluid with a drop of distilled water and soon finds it teeming with bacteria. Which is likeliest, that the drop contained germs, or that it modified favorably the molecular state of the liquid ? Of course, the former supposition.

Thus nowhere, the reader sees, is there a truly crucial test of the two explanations. Every experiment appeals to alternate possibilities, and the aim of experimenters now should be to multiply facts to give to one or the other of these a clear balance of probability. Whichever gets this, be it panspermism or evolution, will no doubt be adopted as truth. Often an experiment will seem to strengthen both sides. Thus, — to take a recent very beautiful one by Chauveau, — rams in France it appears are sometimes converted into wethers without rupturing the skin by twisting the spermatic cord. This occludes the artery, and if the animal is healthy, the part cut off from blood undergoes fatty degeneration, without inflammation or gangrene. But when Chauveau injected a putrid fluid full of vibrios into the ram’s blood long enough before the operation for the animalcules to reach every organ, and then twisted the artery, the gland putrefied. He then filtered carefully some of the fluid and injected into another animal the liquid alone without the vibrios. In this case the gangrene did not take place. This proves, he thinks, the absolute dependence of putrefactive changes on a supply of animalcules from without, and is certainly very brilliant as far as the particular case goes. But Bastian can say, Let us distinguish! This gland, I admit, under these circumstances, cannot engender animalcules of itself But you have no right to make the case universal. And your result seems to prove, moreover, that vibrios have no germs. No filter can hold back germs of the minuteness which panspermism postulates. If there had been any in your case they would have passed through with the liquid and inoculated the testicle, which, the first experiment shows, was inoculable. I have a right therefore to appeal to this experiment as disproving the existence of those invisible bacterium and vibrios germs which no one can directly observe, but which you erect as a dogma.

And so the matter hangs while observations are multiplying. The day is past when the behavior of one or two fluids could be taken as types by which the general problem might be settled. Hundreds of fluids will become alike good niduses, yet they differ enormously in the influence which physical circumstances have upon their productivity. Degree of heat, length of exposure, pressure, presence or absence of air, specific gravity, warmth of incubation, are all factors of fatal or vital moment, but to no two fluids in just the same way. This diversity is accounted for by the panspermatists by the supposition of a corresponding number of germ species, each with its peculiar physiologic idiosyncrasy. Thus, if 60° C. renders saline solutions barren, though they be open to the air, while Professor Wyman once found a mutton-juice flask fertil e after 1520 C., we may suppose a peculiar salamandroid mutton-juice germ to exist everywhere, but to find in a saline solution no fit nidus ; while we must suppose that the germs which saline solutions suit are both killed by a heat of 60° in such fluids, and are not carried about alive by dry air.

Bastian ingeniously explains the different effects of different fluids under the same circumstances, and vice versa, by supposing the power to produce an organism by archebiosis to be only an intensification of the power to make a germ hatch or to nourish an adult. And he divides all substances into three classes, corresponding to as many degrees of this fertility or fermentability. In the first and highest class (of which a turnip infusion, neutralized and containing a speck of cheese is the best known type) the power is absolute and the liquid is fertile of itself. In the second degree we find a stimulus from without needed. But that of a dead ferment will do, any speck of dead organic matter such as the air is filled with may start the molecuular reconstruction by its own “ motordecay,”as in Liebig’s theory of catalysis. A great many infusions and liquids are contained in this class, all in fact which will not keep in the air after exposure to a higher temperature than 600 C., which is supposed fatal to germs. The success of Pasteur’s whole set of experiments (straining air through cotton or flexed tubes, taking it from mountain-tops and vaults, or calcining it) is explained by the exclusion of this indifferent organic dust, not germs as Pasteur thought. Substances of the third or lowest degree of fermcntability need actual inoculation with infusoria before they can produce. Such are saline fluids as regards bacterium production. The surrounding conditions may make a given fluid pass from one class into the other. Thus in tight-stopped bottles which they fill, simple turnip infusions are of the third degree ; in flasks communicating with the air by a tube bent many times, of the second ; while in vacuo they are of the first.

Now here again the issue is one between probabilities. And at the first glance both Dr. Bastian’s theory and that of an immense germ fauna or rather flora struggling for existence 1 lie open to rather similar objections. The fact for both theories to explain is the same, namely, that the difference between, barrenness and fertility in a liquid depends on very minute physical and chemical circumstances. The theories differ in their definition of what it is in the fluid upon winch these varying circumstances bear, and bearing make or mar the result. Pasteur & Co. call it germs and their viability. Bastian calls it determinate possibilities of molecular re-groupment. Now Bastian may say to the friend of germs, “ What you postulate in each particular explanation is at variance with what we see in the general total of cases. You require an exact fit between germ, moment, and nidus before evolution can take place. Yet we find everywhere, when we intentionally inoculate with infusoria, that they are not so squeamish, but almost indifferent about their habitat ; that is, any nidus may be fertilized at any moment by a drop from almost 2 any source.”Whilst the friend of germs can retort, “ So does the general look of facts contradict your theory of the necessity of a sharply defined adjustment of the molecular state. How can the exact state desiderated be present alike in all the infinite variety of fluids which may be niduses,—fluids differing from each other as much as ammonic tastrate solution and beef-juice,— and yet be made to abort in a given fluid by so slight a change as five minutes more of heating, or a degree of rise in the thermometer, or a few shades more of density or pressure ?”

Appeals again to probability! The panspermatist may defend himself by saying that germs do not behave as adult infusoria. “ These latter are what you sow, and to these the nidus is to a certain extent indifferent. But their germs need an exactly propitious soil; as a chicken can live and a hen lay under circumstances in which no egg will hatch.” And the evolutionist may quote Huizinga (Pflüger’s Archiv. June, 1873) : “Time may show that the characteristic properties of portoplasm flow rather from its physical molecular structure than its chemical composition, and that the latter may within certain limits vary” ; and go on to say, “ Fluids of very different chemical composition may offer this structure at certain moments of their existence, but not at others, and so the production of life depend more on the moment being realized than on the fluid which shall realize it.” 3

But a truce to explanations and counterexplanations ! When we get enough data, the more probable hypothesis will readily enough appear. And we have left ourselves no space for telling what some of the most important recent achievements in the way of data are. We may say however that one fact is now pretty clearly established : the air is a less sure ally to panspermism than was supposed. Exposure to air is not necessarily fatal to the purity of a nidus. Saline niduses may be left open almost ad libitum after heating above 60°. And Lister found that he could cover and uncover a variety of organic fluids for a few seconds, and even transfer portions from one vessel to another, without the air inoculating them as much as twice in sixty times. This disarms to some degree the reproach of having failed thoroughly to exclude air germs, which has so often been thrown at successfully fertile flask experiments. Lister himself makes this reproach as regards the fermentation of milk, which many investigators, including Pasteur, found fertile after boiling ; milking a cow with carbolized fingers, from a carbolized udder, into a superheated glass which had been allowed to cool under certain precautions, he found that once out of eleven times it kept unaltered, though unboiled for six months. And this once, he says, suffices to prove the inalterability of . milk per se. (Nature, July 10 and 17, 1873.) Boiled milk he easily kept unaltered, and so did Roberts. (Ibid., February 20, 1873.) This contradiction only shows that we need more observations on milk ; Lister’s interpretation of his result seems inadmissible, for his bold indifference to atmospheric contamination in one half of his experiment renders nugatory his extra-scrupulousness in the other half. Bastian reports cases of flasks containing turnip juice and urine into which cold air had been allowed to penetrate, but which remained barren.

Lister also found that bacteria which appeared in milk refused to grow when transplanted into egg-water and urine. This is very important if true ; for it will show real idiosyncrasies among bacteria, and strengthen the hands of the germ theory very much, whilst the other observations of the same Lister reported in the same paper, showing how organisms have no intrinsically distinct tendency to development, but may change their forms when placed in different media, will reinforce Bastian’s notions about heterogenesis, and have an opposite effect on the germ theory.

The putrefaction with vibrios, etc., of eggs within the shell has been a sort of stumbling-block to the germ theory. But lately Jayon (Comptes Rendus, 21 Juillet, 1873) reports that he has found animalcules in the oviduct of fowls; in which position there is no doubt they may be inclosed within the shell while it is forming, and afterwards multiply.

But we must close abruptly. If the reader will remember the principal subproblems into which we have seen the total question resolve itself, he will, we are sure, find no difficulty in following and thoroughly understanding in their bearing the new observations of fact which every month will probably continue to bring forth in this most interesting field.

  1. Any experiment showing an inhibitive effect of infusoria upon each other’s growth when sown together in a nidus would be important in establishing this struggle of life conception of their status.↩
  2. “ Almost ” : see Lister’s observation, farther on.↩
  3. So that the dead organic dust particles which Bastian says his second class of fermentables require as a stimulus may while in that state start a process which would be beyond their power if previously dissolved and heated in the fluid.↩