conspectus: agents of transmission 25 



Birds probably transmit some of these diseases on their 

 feet or in other ways. In connection with the bud-rot of the 

 coconut palm in the West Indies, I suspect the turkey-buzzard, 

 but the evidence is not complete. Long since, Merton B. Waite 

 obtained (once in Florida, once in Maryland) the strongest 

 kind of circumstantial evidence going to show that pear blight 

 may be spread by birds. 



Respecting insects, molluscs, and worms, the evidence is 

 complete. They often serve to carry these diseases. I have 

 summarized our knowledge in another place ^ and will here 

 content myself with a brief statement calling renewed atten- 

 tion to the subject. 



We had very good evidence of the transmission of one bac- 

 terial disease of plants (pear blight) by insects long before the 

 animal pathologists awoke to the importance of the subject, ^ 

 but it cannot be said that they have ever paid much attention 

 to it, although it antedates by two years the work by Theobald 

 Smith and Kilborne showing that Texas fever is transmitted by 

 the cattle tick {Ixodes bovis Ry.). That discovery also belongs to 

 the credit of the United States Department of Agriculture, and the 

 two together may be said to have laid broad and deep the foun- 

 dations of this most important branch of modern pathology. 

 Waite isolated the pear blight organism, grew it in pure cultures 

 and proved its infectious nature by inoculations. With such 

 proved cultures he sprayed clusters of pear flowers in places 

 where the disease did not occur and obtained blossom-blight, 

 and later saw this give rise to the blight of the supporting branch, 

 found the organism multiplying in the nectar, and re-isolated 

 it from the blighting blossoms. On some trees he restricted the 

 disease to the sprayed flowers by covering them with mosquito 

 netting to keep away bees and other nectar-sipping insects. On 

 other trees where the flowers were not covered he saw bees visit 

 them, sip from the inoculated blossoms and afterwards visit 

 blossoms on unsprayed parts of the tree, which then blighted. 



1 Smith, Erwiu F. : "Bacteria in relation to plant diseases," Carnegie Inst. 

 Washington, Publ. 27, Vol. 2, p. 40, 1911. 



2 Waite, Merton B. : Results from recent investigations in pear blight, Bot. 

 Gaz. 16, 259; Am. Assoc. Adv. Sci., Proc, 40, 315, 1891. 



