BOOKS.
THE DIFFUSION OF ORGANISMS IN THE AIR.*
SURPRISE was expressed in many quarters, when it became' known, a few years ago, that Professor Tyndall, neglecting for a- while the study of purely physical phenomena, was engaged for- nearly three years in laborious investigations into the nature of the organic matter contained in the air. It was thought that the number of qualified inquirers in France, Germany, and, England was already sufficiently great, and that the contro- versies as to spontaneous generation and the germ theory of disease, which were so hotly contested among biologists, might be settled without the intervention of auxiliaries from other de- partments of science. The publication of two memoirs in the Philosophical Transactions for 1876 and 1877 enabled competent, judges to form their opinion on this point; but the appearance of the present volume has afforded to the general public an op- portunity for arriving at the same judgment. Along with the- two important papers in which the observations and experi- ments of two successive years are recorded and their significance- carefully discussed, two lectures and an essay of a more popular character, bearing the titles, "Dust and Disease," "Fermenta- tion," and " Spontaneous Generation," are here included.
The general results of the inquiries in which Professor Tyndalb has taken so prominent a part may be stated in a few words. While, from the nature of the case, spontaneous generation can- not be shown to be impossible, all the observations which were supposed to establish its existence have been proved to be- fallacious, and the doctrine has been finally abandoned by almost all competent men of science. On the other hand, it is no less impossible to define the exact nature of objects so minute as to evade the utmost powers of the microscope, but it is now established that ordinary air contains mul- titudes of organic particles, which under favourable conditions are developed into living creatures, and especially into those called bacteria, whose growth is the necessary concomitant of putrefaction, and which may therefore properly be termed organic germs. It is most probable that there are many distinct species of bacteria, differing among themselves as to their con- ditions of life, and especially as to their power of resisting heat- and other destructive agencies ; but they are all capable of causing putrefaction in organic substances, and, amongst others, that form so fatal to man known as gangrene, of which a remarkable case from his personal experience is recorded by Professor Tyndall, at p. 261 of this volume.
In the establishment of these important conclusions, especi- ally in the overthrow of the doctrine of spontaneous generation, the share borne by Professor Tyndall is large and important ;- and it may be questioned whether, without the aid of one pos- sessing a mastery alike of the methods of physical investigation and the principles of scientific demonstration, the controversy • Buoys on the Floating Matter of the Air, in Relation to Putrefaction and blee- tim. By John Tyndall, Pas. London: Longmans, Green, and Co.
would have been so nearly closed as it now is. The application of light as a means for investigating the condition of the air, was a first contribution of the eminent physicist to the re- sources of the investigator of organic germs ; the proof that the action of gravity in air freed from disturbance is alone sufficient to sift it of organic germs, was a farther important step ; and many ingenious arrangements for varying and con- trolling the conditions of experiment are further to be credited to the eminent author of this volume. But although the im- patient reader may slur over the pages, the part of this work which most excites the admiration of the true man of science, and which will go farthest to increase the permanent reputation of its writer, is the record of the long series of observations contained in the memoir on the vitality of putrefactive organisms, first presented to the Royal Society, and npw republished. It would, indeed, be difficult to quote a better example of the method and the spirit with which a difficult in- vestigation should be pursued, and of the qualities by which success is ultimately attained. When we read what at first seems like a long record of failure ; when experiment after ex- periment is found to give results contrary to reasonable antici- pation, and seemingly inconsistent with previous hard-earned experience, when we go through the tale of the hundreds, nay, thousands, of fresh observations required to test each step in the chain of reasoning which ultimately leads to a consistent conclusion, we feel that it is not only in the contests of active life that energy, caution, perseverance, self-control, along with inborn intellectual gifts, are needed for success.
It may be regretted by some, and especially by those who most admire the works of Professor Tyndall, that he has not found time to use the ample materials at his disposal in the composition of a book, in which the present state of our knowledge on the important matters here discussed should be set forth with that union of scientific accuracy and literary skill for which he is distinguished. The form of the present volume precludes the attainment of such a result. Papers, some of them intended for a popular audience, some for the special and almost exclusive use of men of science, do not fit together so as to give a connected view of the subject-matter ; repetitions are unavoidable, and the topics are not always well arranged, and in a few instances the results of experiments are given with less than the author's usual clearness. It may be safely asserted that a work such as Professor Tyndall could write, if he were so minded, would serve to direct public attention more actively than the present volume is likely to do to subjects of the deepest and most universal concern. It may, indeed, be confidently asserted that there is no matter affecting the physical well-being of our race, with which science is concerned, nearly so important as that which, in the present state of our imperfect knowledge, we call the germ theory of disease. Intimately connected with the objects of Professor Tyndall's inquiry, and frequently referred to in this volume, this subject has excited but a com- paratively feeble interest in the public mind; and even those conclusions which may now be regarded as certain, have appar- ently not much affected the practice of the Medical profession. That all diseases known to be contagious, including most, if not all, epidemics, are caused by the development of organic germs in some part of the human body, is now accepted as a truth demonstrated in regard to some of them, and not open to reasonable doubt as to the rest. The inference drawn by some writers, that a fuller knowledge of the nature and life conditions of the organism causing each specific disease may hereafter enable us entirely to eradicate both the organism and the dis- ease, appears somewhat over-sanguine ; but no one can doubt that such knowledge will lead to improved modes of prevention, and perhaps of cure, which may greatly limit the havoc caused by diseases of this class. Nor will it be a slight gain to rid mankind of the mass of error which even now is accepted by the so-called educated classes in relation to health and disease. When it is clearly understood that a contagious disease can arise only from the development of a special organism that must originate from a previous case of the same disease, care will be directed to the real sources, and ignorant apprehension will be calmed. We shall know exactly, as we do not now know, under what con- ditions the treatment of the sick may be so conducted as not to lead to the spread of the disease among those not already affected, and there will be an end to the unfounded alarms which constantly trouble the life of nervous persons, and which dic- tate many of the useless and vexatious regulations which, under the name of quarantine regulations, interfere with the general freedom of trade and international intercourse. To cite a familiar instance, the opinion still sanctioned by eminent medical authorities, that typhoid fever arises from bad or deficient drainage and the escape of an ill-defined substance
called sewer-gas, is utterly rejected by modern science ; and the knowledge that this plague is as much the result of the in-
troduction into the human body of a specific germ as a crop of wheat or oats is of the sowing of the seed by the farmer, at once changes all the current opinions as to systems of drainage, and the right mode of combating the spread of the disease.
If the prospect of future benefits to our race from the further extension of our knowledge is thus vast, it is equally evident that a prodigious amount of careful research must be accom- plished by men of science, before these benefits can be completely attained. Professor Tyndall has been careful to recognise the achievements of the men who have led the way in this branch of inquiry, and whose labours must serve as models for those who are to succeed them. Foremost he rightly places the illus- trious name of Pasteur in France, and, not to specify many others, those of Cohn and Koch in Germany. To the patient. investigations of the last-named physiologist we owe the almost complete knowledge now gained of the destructive organism which is the origin of splenic fever, whose ravages in the east of Europe have been so formidable, that in the single government of Nov- gorod it carried off over 56,000 head of cattle and 528 human beings in course of three years. The labour expended by Professor Tyndall in setting to rest the doubtful question whether or not the germs of bacteria are carried by the air, or, as some eminent men concluded, they are always conveyed by water, affords a measure of the difficulties remaining to be over- come in regard to the organisms producing disease. It is evident that the question of primary importance in each case is to determine in what way the spore or germ can be diffused, and until this is definitively settled, every effort to combat it must be uncertain in its effects. All that we can now say is that it seems probable that some of these germs may be conveyed by the air even to considerable distances, that others are solely or mainly conveyed by water, others by the bloodor the secretions of animals ; while others apparently. attach themselves to the surface of solid bodies, especially organic textures, and are pro- pagated by actual contact with the skin of men or animals.
These, however, are mere conjectures. For each disease we require a new Pasteur, or Tyndall, or Koch, perhaps even the combined labours of many such men, before the efforts of the physician can be guided by the requisite knowledge. In the mean- time, all dogmatic assertions, such as have too often been uttered by men eminent in medicine, must be considered rash, and likely to do mischief. Some years ago, when the alarm as to the communicability of cholera by contagion had taken un- reasonable proportions, it was authoritatively announced that the disease is never under any circumstances contagions, and in consequence, all precautions based on the opposite belief were in many quarters laid aside. There is, perhaps, no formid= able disease of which so little is certainly known as cholera. That its diffusion depends on that of a specific organic germ is a conclusion not yet completely demonstrated, but so nearly certain, that it must be admitted as provisionally true ; but until the life-history of that germ is fully known, every other statement about it can be considered only more or less pro- bable. That contagion, in the sense of actual contact between the cholera patient and the person or substance conveying the disease, is not the ordinary or frequent mode of diffusion, may be held as a highly probable opinion ; but the absolute denial of contagion has been negatived by many well-established facts, some of which, preserved, or rather lost, in the wilderness of Parliamentary papers, fixed the attention of the present writer many years ago. Towards the close of the famine period in Ireland, about the year 1850, several cases of cholera occurred in seaport towns of that country. Apprehending the danger of an outbreak of such a disease among a population reduced by previous privations and unwholesome food, the Poor-Law Com- inissioners devoted the utmost attention to the subject. They supported the local authorities in several places in the estab- lishment of a virtual system of quarantine, and caused special inquiry by competent medical men to be made in each case of the new appearance of the disease.
Many of the facts then brought to light were afterwards embodied in a set of papers presented to the House of Commons. One instructive case may be here recalled to memory. A report reached Dublin to the effect that a woman had been seized with Asiatic cholera in a place at the western end of the county of Cork, and had died within a few hours. No other case was known to have occurred in the surrounding region or anywhere nearer than the city of Cork, about 60 miles distant, whence a few cases had been reported. The medical inspector, who at once proceeded to the spot, ascertained that the deceased was the wife of a carrier, who plied his trade between Cork and the neighbourhood of Bantry. The man had returned home on the evening preceding the woman's death ; she had been seized during the night beside her husband, who was in no way affected, and died on the following day. Pursuing his inquiry, the in- spector went to the lodging-house in Cork where the man had passed the night preceding his return home, and there dis- eovered that a man had died of cholera two or three days before, in the bed used by the Bantry carrier.
Facts of this nature should impress medical men with the need of extreme caution in the expression of positive opinions on the diffusion of epidemic disease. As to most of them, they are yet in a state of darkness, or at best of dim twilight, in regard to the most important facts ; and light can be obtained only by long continued, persevering, and cautious scientific inquiry. If there be one lesson which more than every other should be drawn from the researches recorded in the present volume, as well as from all the other successful efforts in the same direction, it is the need of constant, ever-suspicious caution, on the part of the inquirer. In illustration of this saying, we should deal- Aerate a special investigation into the use of cotton-wool as a means of completely filtering air from suspended organic matter. Its use for this purpose has been extensively adopted, both in the researches of Professor Tyndall, and in the antiseptic treatment pf surgical cases for which the world is mainly in- debted to our countryman, Professor Lister. Even supposing it to be proved that air, however heavily charged with germs, is -completely freed from them by passing through a plug or a thick layer of cotton-wool, may it not happen that when cotton is used in air of this character, germs may be contained in the air enclosed on the inner side of the plug or layer, which being little or not at all filtered, may be conveyed to the infusion or the wound, and may not this account for some of the anomalous eases recorded in this volume, and encountered by other ob- servers P
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