180 AMBEICAN POMOLOGY. 



try. Early in the present century it prevailed extensively 

 in New England, coincidently with the spotted fever, and 

 other disorders of a low grade of action, which at that 

 period swept epidemically over that region of the country. 

 It was a popular opinion that all these diseases, both of the 

 human family and vegetable kingdom, arose from one 

 cause ; — an opinion not, however, tolerated by medical 

 men and men of science in that day. 



" Various theories have been advanced to account for 

 the origin of this blight. Insects, frozen sap, electricity, 

 excessive evaporation, and exhaustion of the soil, have, at 

 different times, been assigned as the cause. Investigation 

 of each fails to meet and explain the phenomena attendant 

 on the rise, progress, and results of that disease. It is 

 time they all should be abandoned, and that researches for 

 a cause be extended in some other direction. 



" As a starting point in this undertaking, I will suggest 

 another hypothesis, which may perhaps explain the pa- 

 thology of the blight, and call into use an effectual reme- 

 dy or preventive. Pathology, Dr. Webster defines to 

 be ' the doctrine of the causes and nature of diseases.' 



" 1. The Pear-tree blight is produced by the poisonous 

 impression of the seeds {aporules) of a microscopic fimgus, 



"2. Several combinations of iron, especially the sul- 

 phate {copperas), will, to some extent, counteract that 

 impression. 



" It will be understood that these two propositions are 

 merely hypothetical. If sustained by analogies, subse- 

 quent observations, and experience, they will be accepted 

 as truths ; if not thus sustained, they will of course be 

 rejected. 



