The third question is: What was the disease which carried off one-half of the Plymouth Colony during the first four months after the landing. In answer to this question only plausible conjectures can be made. Various theories have been suggested by medical men and others, but unfortunately insufficient data as to the symptoms and general characteristics of the epidemic have been handed down to us to enable any definite diagnosis to be made. Some have suggested smallpox, and some yellow fever, some cholera and some quick consumption. Some also have raised the question whether the germs of the disease, which swept off the Indians living in Plymouth four or five years before, still lurking in the soil or in vegetation, might not have retained sufficient vitality to develop in the human system. This last suggestion would afford little satisfaction, for the question would remain unsolved as to the nature of the disease. After much thought given to the matter, I have come to what I think is the most natural conclusion, that the disease was what was well known in the days of Irish immigration, before ocean steam navigation was available, as ship fever. Many readers will remember that packet ships and transient vessels were constantly arriving at New York and Boston, crowded with immigrants—after long passages from England, and that long confinement below deck resulted frequently in the breaking out of ship fever and caused serious mortality. The voyage of the Mayflower from Southampton to Cape Cod harbor was more than ninety days in length, and during that time imperfect ventilation and inadequate nourishment in a vessel of only one hundred and eighty tons, carrying within her walls one hundred and twenty crew and passengers, must have furnished all the conditions necessary for the presence of that terrible infection, which in our own day was so fatal to the immigrants from Ireland.