1 78 Lectures on Bacteria. [§ xiv. 



the cells, and ultimately emerging through the bursting epi- 

 dermis. Attempts to communicate the disease by inoculation 

 have not yet been successful, nor has the life-history of the 

 Bacterium been at present thoroughly worked out. 



J. Burrill, of Urbana, in the state of Illinois, describes a 

 disease in pear-trees and apple-trees, known by the indefinite 

 name of ' blight,' and attributes it to the attack of a 

 Bacterium, a rather elongated Micrococcus, M. amyjovorus, 

 Burr., the cells of which are about i /u. in length. The disease, 

 which destroys the bark, is at first narrowly locahsed, but may 

 spread and form a ring round the branch or stem which it 

 attacks, and may then prove fatal to it. Burrill found that the 

 Micrococcus had penetrated into the cells of the diseased part, 

 and that as it developed the normal contents of the cells, 

 especially the starch, disappeared, while ' carbonic acid, hydrogen 

 and butyric acid' were formed. Numerous attempts at inoculation 

 by introducing the Micrococcus into small incisions or punc- 

 tures in the bark of healthy pear-trees and apple-trees resulted 

 in the communication of the disease. Arthur has confirmed 

 Burrill's observations and given further proof that his Micro- 

 coccus is a facultative parasite, producing effects pecuUar to 

 the species. This disease of pear-trees, as far as I am aware, 

 is either unknown in Europe, or has not been investigated. 



From some very brief statements of Burrill it would appear 

 that diseases caused by Bacteria also occur in the peach-tree, 

 the Italian poplar, and the American aspen. 



Prillieux gives a short description of a change which some- 

 times takes place in grains of wheat ; this change which is recog- 

 nised by the rose-red colour which it produces, advances pari 

 passu with the development of a Micrococcus, which destroys 

 the starch-grains, the glutinous contents of the peripheral cell- 

 layers, and to some extent the cell-membranes as well. Dis- 

 organising operations of the Micrococcus are thus distinctly 

 disclosed. Its real significance as an exciting cause of disease 

 cannot be certainly determined from the few published state- 



