It is the almost universal opinion of those who have had the opportunity of widest observation that epidemic dysentery arises from, or is due to, a specific cause, a miasm, a malaria (in its wide etymologic sense, bad air), which emanates from the soil. The simultaneous sudden attack of great numbers under the most diverse surroundings admits of explanation in no other way. But the precise nature of the morbific agent is still unknown. The similarity of epidemic dysentery to malaria would indicate the existence of a low form of vegetable life, a schizomycete, as the direct cause of the disease. But the proof of the presence of a specific parasite or germ is still lacking, and though its speedy disclosure by means of the solid-culture soils may be confidently predicted, it cannot, in the light of existing knowledge, be declared as yet.
Especial difficulty is encountered in the study of micro-organisms in diseases of the alimentary canal because of the myriad variety in enormous numbers found in healthy stools. Decomposition and fermentation both begin in the large intestine, so that the feces swarm with the bacteria and torulæ productive of these processes. Woodward declares that his own observations have satisfied him that "a large part of the substance of the normal human feces is made up of these low forms in numbers which must be estimated by hundreds of millions in the feces of each day," bacteria, micrococci, and torulæ being found "floating in countless multitudes along with fragments of partly-digested muscular fibres and other débris from the food;" but while the torulæ are increased, the other micro-organisms, bacteria, etc., do not appear to be more numerous in the stools of dysentery than in healthy feces.
The doctrine that dysentery depends upon parasites is very old in medicine, and included animal as well as vegetable growths. Langius (1659) declared that swarms of worms could be found in dysenteric stools, and Nyander (1760) went so far as to call dysentery a scabies intestinorum interna; which extravagant conception would have speedily met with merited oblivion had not his preceptor, the great Linnæus, incorporated the Acarus dysenteriæ into his Systema Naturæ. Sydenham about this time (1670) expressed a much clearer conviction of the cause of the disease when he spoke of "particles mixed with the atmosphere which war against health and which determine epidemic constitutions."
Baly (1849) first proclaimed the idea of a vegetable fungus, similar to that described by Brittan and Swayne in cholera, as the parasite of the disease; and Salisbury (1865) described algoid cells and species of confervæ as occurring abundantly in all well-marked cases. Klebs (1867) found spore-heaps and rod-like bacteria in the stools of dysentery as in cholera, but maintained that those of dysentery were larger and thinner than those of cholera. Hallier (1869) maintained that although there was no morphological difference in the micro-organisms of the stools of dysentery, typhoid fever, and cholera, he was able by culture-experiments to develop the micrococcus of dysentery into a special fungus, which he called Leïosporium dysentericum. Busch (1868) demonstrated nests and colonies of micrococci, as well as mycelium, in the villi and among the glands of the mucous and submucous tissues in the cases of dysentery from Mexico which he examined, but Heubner (1870) was able to disclose them in equal numbers in preserved preparations or fresh contents of healthy intestines. Dyer4 (1870) believes that the parasites constituting the mildew or sweat which forms a viscous pellicle upon fruit is the agent which directly produces and propagates the disease. Mere immaturity of fruit gives rise only to diarrhoea. This parasite occurs in some years more than others, which accounts for the irregularity of occurrence of the disease. He avers that it is only necessary to clean fruit, more especially plums, to prevent the disease. This suggestion merits place only as a curiosity in the history of the mycology of dysentery.
4 Journal f. Kinderkrankheiten, No. 317.
More important are the results of the experiments of Rajewski (1875), who found the lymph-spaces filled with bacteria, and who was able to produce a diphtheritic exudation upon the surface and in the substance of the mucous membrane of the colon by the injection of fluids impregnated with bacteria into the bowels or blood of rabbits; but this result was only obtained when the mucous membrane had been previously irritated or brought into a catarrhal state by the introduction of dilute solutions of ammonia. It remains for subsequent investigation to confirm these highly significant conclusions, which, when properly interpreted, may explain the action of the predisposing and exciting causes of the disease. Rajewski's bacteria, it is needless to state, were simply the bacteria of common putrefaction. Lastly, Prior (1883) describes a micrococcus as the special micro-organism of dysentery, and Koch (1883), in prosecuting his studies of cholera in Egypt, remarks incidentally upon a special bacillus which he encountered in the intestinal canal in dysentery, though he is as yet by no means prepared to ascribe to it pathogenetic properties.
The question of contagion hinges upon the specificness of the disease, and cannot be definitely determined until this problem is finally solved. The old writers believed in the contagion of dysentery. Helidæus declared that he "had often seen it communicated by the use of clyster-pipes previously used in the treatment of those suffering with the disease, and not properly cleaned;" and Horstius and Hildanus speak of the communicability of the disease from the latrines contaminated by dysenteric excreta. Van Swieten maintained that washerwomen contract it, and that physicians and nurses might be affected. Degner saw the disease spread from street to street in Nimeguen, while every one who came in contact with the disease became affected. Pringle observed it spread from tent to tent in the same way; and Tissot went so far as to declare, "Sil ya une maladie veritablement contagieuse c'est celle ci." Ziemssen believed that the disease is only contagious when the element of crowd-poisoning is superadded; and Heubner states that trustworthy army surgeons in the Franco-Prussian War frequently saw infection occur when many severe cases were heaped together in a small space. Under these circumstances thorough disinfection of the privies checked the spread of the disease. But it was the universal testimony of these surgeons, as also of our own surgeons of the Civil War, that the disease was never transported to the civil population by any of the tens of thousands of cases on their return to their homes.
By most modern writers dysentery is given a place, in respect to contagion, between the exanthematous maladies, typhus and scarlatina, which are without doubt contagious, and the purely miasmatic diseases, malarial and yellow fevers, which are without doubt not contagious. Dysentery is ranked with typhoid fever, which is contagious, not by contact with the body, but with the discharges. It is not a question in dysentery of epithelial drift or pulmonary exhalations, but of ingestion or reception of the dejecta of the disease. By this observation it is intended to convey the impression that dysentery, like typhoid fever, is mostly spread in this way, but the reverse may be true; it may be spread, like yellow fever and malaria, by poisons in the air. But dysentery, as has been repeatedly remarked, is only a clinical expression of a disease which may be caused in many ways; and among these causes, least potent perhaps, but present nevertheless, is contagion. For, not to mention the epidemics which were undoubtedly spread in this way, as among the Allies at Valmy in 1792, among the French in Poland in 1807, and in the hospital at Metz in 1870, dysentery has been directly communicated by the use of clysters, bed-pans, and privies in a most unmistakable way.
According to Eichhorst, the poison of dysentery is endowed with extraordinary persistence of duration or tenacity of life in the stools; for "observations are recorded where dysenteric stools have been emptied into privies, and individuals employed to clean them out after the lapse of ten years have been infected with the disease. These observations go to prove, of this as of other similar affections (typhoid fever), that the virus or microbe of the disease finds its most favorable nidus in vaults, cesspools, sewers, etc. When the poison is exposed to the air it is much more speedily destroyed, but is in the mean time of course a possible conveyer of the disease." Fayrer quotes from an anonymous writer, "whose views are as remarkable for their force as for their originality," the rather extravagant assertion that "if human excrement be not exposed to the air there can be no dysentery."
Knoewenagel has recently5 opened up a new series of reflections in his suggestion of a possible direct infection of the large intestine per rectum, where the disease usually begins and is mostly best expressed. He calls attention to the fact that people who suffer with constipation indulge in longer sessions at stools and induce in straining efforts a degree of relaxation of the rectal mucosa. The mucous membrane at its orifice may become at the same time abraded by hardened fecal masses, to leave open surfaces or crevices upon which germs may lodge. Moreover, aspiration follows the efforts at expulsion, and the air with its particles is drawn directly into the rectum, thus affording all the conditions for immediate or direct infection.