Читать книгу: «Chambers's Journal of Popular Literature, Science, and Art, No. 724», страница 5

THE GERM THEORY AGAIN

We have on several occasions alluded to the Germ theory, by which is meant the theory that invisible germs, capable of producing animalculæ and of spreading disease are constantly floating in the atmosphere – and that the more impure the air the greater are the number of these germs. We revert to the subject, because it is debated in all quarters, and it is as well that our readers should know something of what is causing so much controversy. Some surgeons distinguished as operators are great believers in the Germ theory; so much so, that before beginning, for instance, to cut off a leg, they cause a certain germ-killing liquid to shower like spray near the part operated on; by which, as is alleged, the wound is kept free of anything noxious. Whether there be germs or not, the use of disinfectants in the air is said to be beneficial. Notably the celebrated carbolic-acid plan of Professor Lister has met with marked success, and is practised by the greatest surgeons of our time. But though the air certainly contains something which favours decomposition, it is by no means yet proved that that something is made up of germs.

Professor Tyndall has been the principal advocate of the Germ theory, and has written some papers strongly in its favour. Professor Bastian takes an opposite opinion. He thinks that living organisms may originate in disease by spontaneous generation. His notions are that if germs are continually floating about in the air, they would drop everywhere and anywhere alike. This argument applies more forcibly to the fact which Dr Bastian discovered – namely, that he was able to get life in flasks containing inorganic solutions, but that he always failed if such solutions were not made up of salts containing oxygen, hydrogen, carbon, and nitrogen; that is to say, of the elements of life. If the organisms are really the result of a molecular arrangement of the 'mother-liquid,' we should expect to find them only in those fluids which already contain the elements necessary for their composition. Three speculations are involved in these experiments: on the one hand, that low forms of life do occasionally arise by spontaneous generation; on the other hand, either that the heat which is usually considered destructive of life and germinating power is in reality nothing of the kind; or that Dr Bastian's experiments were incorrectly performed.

Since the publication of Dr Bastian's observations, a very lively controversy has been carried on in scientific quarters between the supporters of the germ theory and of the theory of spontaneous generation. Dr Bastian's work was conducted with great care and in the presence of some distinguished authorities. Dr Sanderson, on the other hand, found that upon increasing the heat which is applied to the flasks, no organisms were produced; but until we have reason to doubt the generally received opinion as to the amount of heat necessary to destroy life, this result may be equally well explained according to either of the two theories.

Dr Bastian insists that the organic solutions in his own flasks are not found by him to undergo putrefaction where every precaution is taken for withholding the entrance of air. Thus a simple piece of cotton-wool, which acts as a kind of sieve, will when placed in the mouth of a flask prevent decomposition. Professor Tyndall has invented the most ingenious contrivances for illustrating his views. In one case he employed a chamber the walls of which were covered by a sticky substance. The particles of dust in the air were allowed to collect and adhere to the sides, and the air in the vessel, as shewn by its non-reflection of a beam of light, was rendered comparatively dustless. Flasks were now introduced, and they remained for a long period free from organisms. On repeating some of these experiments this year, however, Professor Tyndall found that many of the infusions which had previously been preserved from putrefaction with ease, were now found, when placed under the same conditions, to swarm with life. Still he refused to believe in 'spontaneous generation,' and preferred to consider that the production of life in his flasks was due to some fault in his experiments, and that the air of the Royal Institution was not so pure this year as it was last. Instead, therefore, of introducing his fluids by means of an open pipette, as he had previously done, he now made use of a 'separating funnel,' and by this means the fluids found their way into the flasks without exposure to the air. The result of these precautions was that no organisms appeared. The objection, however, that we have to find is, that no guarantee can be given that will enable us to ascertain whether the air is really free from particles of organic matter or not. Last year the air was considered to be pure because moteless; but this year, though moteless, it was found to be impure.

Professor Tyndall and his friends are so exceedingly confident in the power of the germs of the atmosphere, that they attribute to their influence every known case of putrefaction; and they do so because they believe that they have proved that whenever the air can be excluded from a putrescible fluid, putrefaction will not take place. But Dr Bastian has succeeded in producing life out of organic infusions from which the air has been excluded, and which have been previously raised by him to temperatures hitherto considered by scientific authority as fatal to life. Thus the question resolves itself into this: What is the exact point of heat which kills the germs of bacteria? At present we do not know, and we have therefore no right to make any supposition upon this point in favour of either of the two theories.

Since Dr Bastian's experiments were first made public, the holders of the Germ theory have gradually raised what we may call the thermal death-point of bacteria, in order to explain away the results of his experiments by the light of their own theory. If Dr Bastian's fluids did develop life, they say, the germs must have entered into them by some means or other; and if he superheated these fluids, the fact of the germs surviving the process shews that they must be possessed of greater enduring power than we have given them credit for.

Curiously enough, Professor Tyndall declares that frequent applications of a low degree of heat, and applied at intervals, have a far greater 'sterilising effect' than a single application of a high temperature. For a given fluid may contain germs of all ages. If such a fluid be boiled for a considerable time, all the germs of recent formation will be killed; but those of a greater age will merely be softened, but still capable of reanimation. If, however, the fluid be heated for a short time only, the recent germs will be destroyed, while an older crop will be liberated. A second application of heat destroys this second crop, and brings a third into play. Further heat will awaken successive crops, until at length a point is reached when the toughest germ must yield. This is certainly a most ingenious explanation of the difficulty.

A very interesting contribution to this subject has lately been made by Dr Bastian and others; and we will now briefly describe the main results of their researches. It has long been known that slightly alkaline organic fluids are more difficult to sterilise than those which are slightly acid. Pasteur the French chemist says that animal water in its normally acid state becomes sterile at one hundred degrees centigrade; but that if the infusion is first rendered alkaline by the addition of potash, the application of a little more heat is necessary, in order to insure sterility. If we bear in mind the two theories, we shall see that these observations of Pasteur may be explained according to either of them. We may believe that the germs in the infusion are fortified against the destructive action of heat by liquor potassæ; or on the other hand, we may hold that the spontaneous generation of organisms is favoured by the presence of an alkali. Acting upon these data, Dr Bastian heated a similar fluid in its acid condition to the temperature of one hundred degrees; so that, according to Pasteur, it was now barren. He then added a quantity of potash sufficient to neutralise the acid, the addition of the alkali thus being made after instead of before the boiling; and he then allowed the fluid so treated to stand at a temperature of about one hundred and fifteen degrees Fahrenheit. In a short time swarms of bacteria appeared.

Dr Roberts, however, considers that this result was obtained because sufficient precaution had not been taken by Dr Bastian to prevent the entry of germs, which might have been introduced by the potash. Accordingly, he filled a small flask with an ounce of the acid infusion, and then sealed up his potash in a capillary tube. The potash was then heated in oil to two hundred and eighty degrees Fahrenheit, and kept for fifteen minutes. The tube of potash was now introduced into the flask containing the infusion, and the flask was boiled for five minutes, and sealed. The flask was now kept for some time in order to test its sterility. When this was ascertained, the flask was shaken, so that the little tube of potash inside was broken, and the potash was thus allowed to mingle with and neutralise the infusion. The flask was now maintained at a low temperature of one hundred and fifteen degrees Fahrenheit, and it remained perfectly clear. And so Dr Roberts concludes that liquor potassæ has no power to excite the generation of organisms in a sterilised infusion. Professor Tyndall repeated these experiments with additional precautions, and obtained similar results.

The general conclusion which is drawn from various experiments by the advocates of the Germ theory is, that liquor potassæ has no inherent power to stimulate the production of bacteria, and that any apparent power of this kind which it may seem to possess is due to the presence of germs within it. These germs they consider are not destroyed until the potash has been raised to the temperature of one hundred degrees centigrade if solid, and to one hundred and ten degrees centigrade if liquid. Dr Bastian, who repeated his former experiments with every possible precaution, found no difference in his results. Moreover, he discovered that liquor potassæ, when added in proper quantities, is just as efficacious in stimulating the development of life after it has been heated to one hundred and ten degrees centigrade, as when it has been heated to only one hundred degrees. Pasteur will consequently have to raise the temperature which he considers sufficient to destroy the germs contained in a solution of strong liquor potassæ to a point still higher than one hundred and ten degrees.

But there is still another proof that liquor potassæ if previously heated to one hundred degrees does not induce fermentation in virtue of its germs, because if only one or two drops be added, the infusion will remain as barren as ever; while a few more drops will immediately start the process of fermentation. Now if the potash really induced fermentation because it brought germs along with it, two drops would be quite as efficacious as any other amount. Finally, Dr Bastian has shewn us that an excess of alkali prevents fermentation, and to this fact he attributes the failure of Pasteur to develop life when he employed solid potash. He had added too much of the alkali.

It is impossible to draw any definite conclusion from these as from the other experiments, until we know the precise temperature which is fatal to germinal life. Dr Bastian indeed thinks that he has been able to shew that bacteria and their germs cannot exist at higher temperatures than one hundred and forty degrees Fahrenheit; but his evidence here is not quite conclusive. He does not deny the existence of germs nor their probable influence in producing life; he merely says that his experiments furnish evidence to shew that in some cases organisms may spring into existence without the aid of a parent. The strong points of his case are, that as fast as his adversaries can suggest precautions to insure the destruction of germs, he has been able to shew life under the altered conditions; and that whenever the supposed death-point of bacteria has been raised on account of his experiments, he has succeeded in obtaining life after having submitted his flasks to the required temperatures. How this most interesting controversy will end, we cannot foretell; but we hope that the further researches of our scientific men upon the subject will ultimately lead to the discovery of the truth. Meanwhile, we observe that Dr Richardson, at the late Sanitary Congress at Leamington, entirely dissented from the theory of germs being the origin of disease, and characterised it as the wildest and most distant from the phenomena to be explained, ever conceived. As no one contests the fact that pure air is a very important factor in promoting health and averting the insidious approaches of disease, people keeping that in mind need not practically give themselves much concern about germs. See that you draw pure air into the lungs. That is an advice to which no theorist can take exception.