228 NINETEENTH REPORT. 



Two copper fungicides were tested^ viz., Ammoniacal copper carbonate 

 and neutral copper acetate. The ammoniacal copper carbonate solution 

 was made as follows: 



Coi:)per carbonate, 1.43 grams. 

 Ammonia 26° Beaume, 15 cc. 

 Water, distilled, 20 cc. 



The great concentration of this solution was necessary in order to 

 obtain in the dilutions the killing point of the spores. In the same way 

 a saturated solution of neutral copper acetate was necessary as a basis 

 for dilution. 



PROCEDURE. 



As has already been suggested the method advanced by Anderson and 

 McClintic has been made the basis for the development of the method 

 of testing fungicides which is recorded in this paper. Radical modifica- 

 tions have been necessary because of the wide differences between 

 bacteria and fungus spores. Briefly stated the method consists in sus- 

 pending in distilled water the fungus spores to be tested. INIeasured 

 portions of this suspension are exposed for definite periods of time to 

 the fungicide to be tested and to the copper sulphate standard. Definite 

 amounts of the spores thus exposed are introduced into tubes of melted 

 agar and then poured into plates. These plates are incubated for four 

 days and then examined for growtli. A constantly recurring trouble in 

 the early stages of the work was the difficulty encountered in introducing 

 a sufficient number of spores into the diluted fungicide for exposure and 

 the subsequent introduction of the exposed spores into the tube of melted 

 agar. A platinum loop of the type used by Anderson and McClintic could 

 not be depended upon to introduce the spores. A platinum spoon gave 

 but little better results. Sterile pipettes graduated to .1 cc. were finally 

 used and gave uniform plantings when .1 to .2 cc. of the dilution were 

 used. A large number of sterile pipettes is necessary for each pipette 

 must be sterilized before being used again. 



Dilutions of the fungicide were made twice as strong as the sub- 

 sequent exposure required. This allowed for the introduction of the 

 spore suspension which was calculated to reduce the strength of the 

 fungicide one-half. 



