222 NINETEENTH REPORT. 



Previous to the work given above, Burrill" described a method in which 

 spores were placed directly in a solution of Bordeaux mixture and after 

 a specified time sprayed on a slide. The determination was made just 

 as in the above method. The two methods seem to be almost alike, 

 yet the results in each were very different. The reason for this great 

 difference is explained by Cavenaugh who gives us the chemical changes 

 in lime sulphur as used in the first method. When the solution comes 

 in contact with the oxygen and carbon dioxide of the air a solid material 

 is formed. The calcium tetra- and panta-sulphides (CaS4 and CaSg) 

 are oxidized to thio-sulphate (CaSO^), and later to sulphite (CaSOg), 

 sulphate (CaSO^) along with some free sulphur and other compounds. 

 In this way insoluble compounds are produced which are many times 

 less effective in preventing spore germination then the solution would 

 be if unexposed to the air. It has been proven, as the chemical analysis 

 would indicate, that lime sulphur is more than two hundred times as 

 effective in preventing s^jore germination when unexposed to the air. 



The other method of determining fungicidal efficiency consists in 

 elaborate and extended field tests. This necessitates the use of experi- 

 mental plots cither large or small, containing the plants to be used, 

 considerable apparatus, much labor and longer or shorter periods of time, 

 depending upon the nature of the plants used. However, no standard of 

 comparison could be worked out as too many uncontrollable factors must 

 be dealt with. 



The work upon which this paper is based has been confined exclusively 

 to the problems of arriving at a satisfactory laboratory method of deter- 

 mining fungicidal values based upon a definite standard. The object 

 was to perfect a method by which various chemicals could be tested, 

 and their fungicidal value determined in terms of some definitely known 

 compound the action of which was sufficiently stable and uniform to 

 merit its adoption as a standard. In this way it would be possible to 

 determine the efficiency of a new or little known fungicide by means of 

 a direct comparison with the standard and thus obtain its relative value 

 as a fungicide. In other words the attempt has been made to perfect a 

 method by which fungicides may be "standardized." To the writers' 

 knowledge no method of this kind has hitherto been formulated. 



In the province of hygienic bacteriology, the problem of the standard- 

 ization of disinfectants has been made the object of extended study and 

 experimentation. 



A method for standardizing disinfectants was advanced by Rideal 

 and Walker*"' in 1903. This method makes use of the varying ability of 

 B. typhosus to resist the action of phenol when exposed to several 

 different concentrations, for definite, though varying periods of time. 



