338 PROCEEDINGS OF THE ACADEMY OF [1886. 



determination of sound and blighting pears, taken from the tree 

 at the same time, shows considerably less sugar in the latter. 



A favorite explanation with horticulturists of the action of fire- 

 blight upon the pear-tree, has been to say that the sap is poisoned. 

 This poison was supposed to be introduced by insects, or to be 

 due to some disorganization of the tissues. Although it is now 

 known that specific bacteria are directlj'^ answerable for the dis- 

 ease, it is yet worth while to see if the old idea of a poison has 

 not some foundation in fact. 



It has been ascertained that certain bacteria produce, during 

 their growth, characteristic poisons which are classed under the 

 name of ptomaines. Most of the ptomaines are non-volatile, and 

 readily soluble in water or alcohol. The chemical tests which 

 are applied for their detection cannot be considered conclusive 

 except when taken collectively. The tests tried below are among 

 the most satisfactory known at present.^ 



A cultivation in infusion of potato, giving about 200 cc. of liquid 

 was filtered, and the filtrate evaporated to a syrup. This was 

 treated with alcohol, and the solution tested with the most char- 

 acteristic test for ptomaines the reduction of potassic ferric- 

 cyanide. Other portions of the solution were successively tested 

 with phospho-molybdic acid, potassio-mercuric iodide, and iodine 

 in potassic iodide, all of which failed to give any distinctive 

 reactions. 



Another trial was made with about 200 cc. of material prepared 

 by cooking a potato in just enough water to cover it, sterilizing, 

 and cultivating the bacteria in it as usual. In four days from 

 beginning of the culture it was filtered ; the residue upon the 

 filter was treated with 100 cc. of distilled water, slightly acidulated 

 with hydrochloric acid, heated to 70C. and filtered. The two 

 filtrates were united and evaporated to a syrup. This was digested 

 in the cold with alcohol containing a little sodic hydrate. This 

 solution was tested as before, and also with platinic chloride and 

 concentrated sulphuric acid, and all with no distinctive reactions. 



A third trial was made with a boiled potato, which had been 

 permeated with the blight. The extract was made by the Stas- 

 Otto method, and the same reagents used as in the last case, with 

 equally negative results. 



1 Cf. Brieger, Ueber Ptomaine, 1885, p. 33, et seq. 



