1886.] NATURAL SCIENCES OP PHILADELPHIA. 337 



readily, or produce a characteristic appearance. Under the 

 microscope the cells are strongly refractive. 



A boiled potato was infected by thrusting a platinum wire, 

 smeared with blight bacteria, into one end. After sixteen days 

 it was cut open. No external change had taken place, and, to 

 the unaided eye, no internal change either ; the odor and texture 

 were still those of a freshly boiled potato. The microscope, how- 

 ever, revealed the blight bacteria in every part of the potato, in 

 irregular motionless masses, and with more than the usual 

 refractiveness. 



These opaque solid cultures have brought out one fact verj'- 

 distinctly, which is, that Micrococcus amylovorus requires a 

 large supply of water for its best development a fact which has 

 an economic bearing. 



Behavior toward Staining Fluids. So far as trial has been 

 made, nothing especially characteristic has been detected to dis- 

 tinguish this form of bacteria from the majority of micrococci. 

 The most successful results have been obtained with a watery 

 solution of Bismarck-brown, especially in cover-glass prepara- 

 tions. These make excellent specimens when mounted in 

 Canada balsam. 



The zoogloea are inclined to be too deeply stained by this pro- 

 cess, and for most purposes they are best studied unstained. 

 They may be well preserved by mounting in glycerine. 



Hematoxylin has also given good results, but has not been 

 found particularly useful. 



Chemical Products. The chemical changes brought about by 

 the activity of the blight bacteria have not yet been fully and 

 carefully worked out. The most obvious product is carbon 

 dioxide, which often passes off so freely from a cultivation as to 

 produce a slow effervescence. Butyric acid and alcohol are 

 formed in very small quantities, if at all. The tests by which 

 these facts have been determined have already been published,^ 

 and need not be repeated here. Vigorous cultures of the bacteria 

 in infusion of potato give no reaction for glucose with Fehling's 

 solution ; and blighting tissues from the tree give no indication 

 by the same test of more than the normal amount of glucose to 

 be found in healthy tissues. On the other hand a quantitative 



^ Rep. N. Y. Agric. Exper. Station for 1885, p. 247 ; and less fully in 

 Amer. Nat., vol. xix, 1885, p. 1181. 



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