Specific Causation of Disease
The preceding review will have made it clear that in the period of earlier slow sanitary reform, although much invaluable work was being done, it was in some measure a groping in the dark, a continuous search for further light while pursuing (or at least advocating in season and out of season) such cleansing and purification of man’s surroundings as were evidently needed, and such segregation of the infectious sick as could be secured in the absence of complete information of the cases of sickness. Happily in the case of Small Pox there was an additional effective protection in vaccination.
With Pasteur’s discoveries was inaugurated a new era in sanitation; the general microbial origin of infectious diseases, inferred from his discoveries, leading to the conclusion that the chief source of disease to others is man himself, and that his surroundings in the main cause disease insofar only as they become a vehicle for conveying disease by direct inhalation of infected dirt (Sax. drit = excrement), or by swallowing specifically infected foods.
The importance of the sanitary engineer in securing pure water supplies and satisfactory sewerage continues. The sanitary inspector’s work in removing nuisances and accumulations, any one of which might be specifically contaminated,[4] and in controlling overcrowding and uncleanliness as well as in other respects, remains indispensable. But the brunt of guidance in the exact prevention of disease, especially of communicable diseases, must necessarily now fall on
the epidemiologist,
the vital statistician, and
the laboratory worker.
Present Limitations of Epidemiology
The epidemiologist must always remain the chief of these three, suggesting and arranging the details appropriate to each investigation, putting together the facts supplied by the two other workers and drawing legitimate conclusions. In conducting his inquiries and in searching for further light on obscure points, he will need to remember Simon’s remarks (Eighth Report of the Privy Council):
In the category of time, far out of human reach, there are circumstances which greatly influence contagion.... These almost cosmic arisings are spreadings of disease or facts of cosmo-chemical disturbance which no mere contagionism can explain.