46 TRANSACTIONS OF THE ILLINOIS 



PEAR BLIGHT AND PEACH YELLOWS. 



BY T. J. BURKILL. 



Since the first finnouncement, three years ago, that the so-called 

 fire-blight of the pear-tree is due to the ferment-action of bacteria, 

 every fact coining to my knowledge upon the subject has helped to 

 confirm the truth of the original statements. There seems to have 

 been no attemjit to disprove the conclusions as published in our 

 Transactions for 1880, nor has there been any evidence produced 

 showing that anything besides bacteria does this deadly Avork in the 

 tissues of our pear-trees. I speak now of what may be accounted 

 trustworthy observation, well considered experiment or scientific 

 investigation, not- the mere guesses which so often pass for knoAvl- 

 edge. Still, there are many who doubt the " bacteria theory," as 

 they choose to call it, and others, some of whom ought to know 

 better, still openly assert that notliing is known of the cause of this 

 disease. It is not now my intention to try to convert any one of 

 either of these classes to my own way of seeing and thinking, neither 

 do I propose now to record additional proofs of the verity of the 

 former reports. That a certain and now well-known species of the 

 minute organisms popvilarly known as bacteria is the real, active and 

 immediate cause of this blight, is a fixed and positive fact — not a fancy 

 nor a theory; a demonstrated and demonstrable truth — not a conjec- 

 ture drawn from data hard to obtain or experiments difficult to 

 repeat. Any one may convince himself of the communicability of 

 the disease from affected to healthy trees, and any one who has the 

 requisite apparatus, and the ability and patience to use it, may as 

 surely convince himself of the existence and action of the exceed- 

 ingly small, but not the less efficient agent in this communication. 

 Not every one can see the mischief working organism, because 

 human eyes unaided are far from being sharp enough for the pur- 

 pose; but it is surely too late in the day to disbelieve things exist 

 because our unaided eyes cannot discern them. The microscope reveals 

 as many additional species of living things, and as many structural 

 components of larger bodies, as were known to man before the inven- 

 tion of this marvelous instrument. So far as disease goes in ani- 

 mals and plants, the whole trend of scientific demonstration shows 

 the increasing appreciation or apprehension of the importance and 

 power of these minute organisms, and he who is disposed to cavil at 

 the ''germ theory '' of disease, simply indicates by this that he is 

 behind the times. Let him make himself acquainted with accessible 

 literature, or much better let him, with rigid accuracy and scrupulous 

 care, repeat the experiments that have been made, and of which the 

 results are recorded, and no dullness of apprehension, nor prejudice 

 of preconceived opinion can possibly prevent the belief that bacteria 

 and their allies are real and positive disease producers. Not all the 



