ACTION OF FUNGICIDES 



259 



(CH3)2N 



=C 



N(CH3)2 



N(CH3)2 



Crystal violet 



CI 



green and crystal violet upon 26 species and isolates of Trichophyton. 

 Malachite green proved greatly superior to crystal violet. Over half 

 the isolates tested failed to grow in the presence of 1 part of malachite 

 green to 50,000 parts of medium, and many failed to grow in the presence 

 of 1 p.p.m. of this dye. Crystal violet allowed some growth in all isolates 

 tested at a concentration of 1 part in 50,000 parts of medium. Placing 

 the inoculum in direct contact with the medium containing the dye was 

 more lethal than placing the agar inoculum plug with the mycelium upon 

 the surface of the test medium. Some other dyes such as methylene 

 blue are also toxic to fungi. Both malachite green and methylene blue 

 inhibit carboxylase (Horsfall, 1945). 



Dithiocarbamates and related compounds. Barratt and Horsfall 

 (1947) have reported extensive investigations on the homologues and 

 analogues of disodium ethylenebisdithiocarbamate (Nabam). In gen- 

 eral, these compounds are formed when primary and secondary amines 

 react with carbon disulfide. The formula for Nabam is given below: 



S H 



H S 



Na— S— C— N— CH2— CH2— N— C— S— Na 

 Disodium ethylenebisdithiocarbamate (Nabam) 



The zinc (Ziram) and ferric (Ferbam) salts of dimethyldithiocarbamate 

 are effective fungicides for the control of certain fungus pathogens. The 

 formula for dimethyldithiocarbamate is given below: 



S 



II 

 (CH3)2— N— C— SH 

 Dimethyldithiocarbamate 



The oxidation product of dimethyldithiocarbamate is tetramethylthluram 

 disulfide (Thiram), which has some value as a seed protectant. 



The dithiocarbamate fungicides, such as Nabam, yield hydrogen sulfide 

 on hydrolysis. This reaction takes place spontaneously in the presence 

 of moisture. The mechanism of hydrogen sulfide toxicity has already 

 been discussed. The second mechanism which has been proposed 

 involves the formation of insoluble mercaptides of certain essential metals. 



