the coli group in the intestinal tract of the domestic fly, where they are capable of surviving five or more days. The same holds good as regards amœbic dysentery. Wenyon found E. histolytica cysts in the intestinal canal of flies that had fed on dysentery stools.
Predisposing and exciting causes.— It seems not improbable that, in conditions of sound health, the several pathogenic organisms of dysentery may exist in and pass through the alimentary canal without attacking the tissues or giving rise to disease. So long as the mucous surface is sound and vigorous, it has considerable power of protecting itself against many such organisms. It is very probably the same in this respect with the dysentery germ or germs as with the cholera vibrio. Probably it is only on the establishment of some condition of lowered vitality, such as may be induced by catarrhal troubles, chill (a powerful excitant of dysentery), irritating food, bad food, constipation, malaria, scurvy, starvation, and so forth— all well-recognized exciting causes —that the dysentery germ can overpower the natural protective agencies and light up the specific lesions. It is a well-known fact that it is in such circumstances that dysentery is most apt to declare itself. Hence the importance of avoiding these things in tropical climates, more especially in the presence of a bad water supply or of an epidemic.
The capacity for latency often exhibited by the germs of dysentery, as of some other intestinal germs, sprue for example, is remarkable. I have encountered cases in which a dysenteric infection (amoebic) contracted in the tropics did not manifest itself for several months after the patient had returned to England. I have also encountered dysenteries that recurred in England at intervals of one, two, and more years up to twenty after infection originally acquired in Egypt.
Influence of age, sex, and occupation.— All ages are subject to dysentery. Children are especially liable to the bacillary form, which in them is often fatal. Occupation has no special influence.
