New York Agricultural Experiment Station. 229 



amount of water the Rhizoctonia was entirely killed. With a total 

 of 297 cultures the efficiency of mercury bichloride in killing the 

 potato Rhizoctonia was 100 per ct. 



The inefficiency of formaldehyde can not be attributed to any 

 single cause, for there are several factors which, when combined, 

 may produce variable results. While making cultures of the sclerotia 

 taken from tubers immersed in formaldehyde solution, it was found 

 that the larger sclerotia were often not moistened throughout. 

 Such sclerotia showed a compact, dry mass of mycelium at the center 

 from which the fungus readily grew. The outer layers, however, 

 were spongy and readily crumbled. In some cases the compact 

 small sclerotia showed the same conditions generally found in the 

 larger ones. The weak penetrative power of formaldehyde may be 

 explained, perhaps, by assuming that the formaldehyde unites 

 chemically with the outer layers of sclerotial tissue forming some 

 substance that retards or inhibits further penetration. This is 

 substantiated by the fact that when tubers are immersed in the 

 ordinary formaldehyde solution for 24 hours the sclerotia are all 

 killed, and it is found that the liquid has penetrated them through- 

 out. Dienes, 18 working on the penetration of formaldehyde gas, 

 has shown that after 14 hours bacteria were killed by the gas pene- 

 trating through a porous porcelain plate 20 mm. thick. The structure 

 and composition of the sclerotia, however, is not analogous to that 

 of a porous plate for in the former the compact mass of resting 

 mycelium is more or less in a state of dessication, which affects the 

 rate of penetration of this chemical. Mercury bichloride, unlike 

 the formaldehyde, penetrates all sclerotia, regardless of size or 

 compactness, in 1§ hours. Such sclerotia are all killed, and readily 

 crumble into small pieces when crushed. In the formaldehyde gas 

 treatment, the temperature and humidity, as usually encountered, 

 do not appear to be factors that influence the efficiency. Mc- 

 Clintic, 19 in disinfecting passenger cars with formaldehyde gas, 

 states that humidity is an important factor in killing bacteria. 

 He maintains that before starting the fumigation the relative humid- 

 ity should not be lower than 60-65 per ct. In his earlier work 



18 Dienes, L. Uber Tiefwirkung des Formaldehyde. Ztschr. Hyg. u. Infections- 



krank. 37:43. 1912. 

 "McClintic, T. B. Pub. Health and Marine Hosp. Ser. U. S. Hyg. Lab. Bui. 27. 



1906. 



