Fig. A. Stony Brook, North Chelmsford, showing in the foreground Tail Race of Woolen Mill, Point of Infection

by Cases No. I and II; in the background, Privy of Foundry, Point of Infection by T. L., (Case No. IV.)

School streets, further enriched by the discharges from the Lowell Hospital and from various privies, and finally added to the excreta from thousands of workers in the mills on the upper level, must have infected the canal water. It should certainly be counted a most fortunate circumstance that the canal water was not more generally used for drinking purposes.

As soon as I had brought to light these unexpected facts concerning canal water, I notified the local board of health, who immediately caused proper placards to be posted in the mills warning the operatives against the use of the canal water for drinking.

Probably the most curious fact developed during the whole inquiry was the discovery that the Lowell Hospital was emptying its sewage directly into the Northern Canal, water from which was, in the manner described, accessible for drinking to thousands of people.

THE WELL-WATER SUPPLY.

There are still many wells in use in Lowell. This is more true, however, of the summer time than of the winter. On account of their greater coolness, well waters are much resorted to in summer, especially by those who have no ice. In winter they are but little used, comparatively speaking, and, as I had been studying certain much-used wells in Lowell in August and September, I had personal and accurate knowledge of the conditions at that season.

In point of fact, some of the wells most resorted to in July and August were almost completely neglected before October 1, and, as I have reason to believe that this was true of most of the wells of the city, I am convinced that the wells could not have been the principal factor in the epidemic of typhoid fever. On the contrary, the epidemic was severest in November, i. e., at a time when the use of well water for drinking purposes had virtually been given up for the season, and the drinking of city water had become, once more, almost universal. I consider it possible that a very few of the cases generally believed to be due to the use of city water or canal water might have been caused by polluted wells, but I failed to find any evidence of it.

In the investigation of the cases of typhoid fever a few were found in which well waters had been used, besides those among the attachés of the mills, who, as we have seen in the previous section, drink much well water. At the same time it was fully proved and will

be shown beyond that, even if polluted canal water had been inoperative, and all mill cases had been due to polluted well water (which we can by no means suppose to be true), there yet remained in the city a notable epidemic among those who had not drunk either canal water or well water, but only the city water.

THE SPRING-WATER SUPPLY.

This, the fifth source of water supply in Lowell, was, comparatively speaking, of minor importance. There were four waters publicly sold in the city as "spring" waters. These I carefully exainined, both chemically and bacteriologically. I found no evidence, however, either in the results of these analyses or in the history of the cases of typhoid fever in the city, that spring waters had had anything to do with the causation of the epidemic. I do not know to what extent these " spring waters" had been used, but I found no evidence whatever that any number of persons who had drunk spring water exclusively had been attacked by typhoid fever. Two or three cases were met with in which spring water was chiefly used, but even these were extremely rare.

CONDITIONS TO BE FULFILLED BY ANY WATER-INFECTION THEORY OF THE EPIDEMIC.

Five distinct systems of water supply in Lowell have now been described. With respect to three of these I found no evidence which made further investigation necessary. The epidemic of typhoid fever in 1890 was not attributable to the Lynde's Hill Reservoir supply, or to the well-water supply, or to the springwater supply. If caused by drinking water of any kind, it must have been by canal water, or by city water, or by both. We have seen that the canal water was so extensively polluted as to suggest that the entire epidemic might possibly have sprung from this source, and this possibility was accepted by some as a sufficient explanation of it. A little reflection, however, was enough to show that even upon this hypothesis it still remained to explain why there was more typhoid fever from this source this year than usual. And, similarly, if the epidemic were to be laid at the door of the city water, it became absolutely necessary to the validity of the hypothesis to show why the city water was worse this year than in other years; and particularly why and how it was worse just before and during