Brown.—Studies in the Physiology of Parasitism. /. 317 
in this respect like oxalic acid ; he chose the latter from its known occur¬ 
rence in the fungus. In one important particular, however, he is at fault, 
inasmuch as the starting-point of his study is a strange misquotation from 
de Bary. The latter he cites for the statement that oxalic acid of 0-3 per 
cent, strength may be found in extracts of Sclerotinia , whereas de Bary 
states categorically that he was unable to demonstrate any free oxalic acid, 
but that this substance occurs solely in the form of its salts (potassium 
or calcium). Smith himself records 3 per cent, oxalic acid in extracts 
of old mycelia, but here he is undoubtedly including oxalates, both soluble 
and insoluble. In the low concentrations employed by Smith, potassium 
oxalate has only a very slow toxic action, and its macerating action is nil at 
all concentrations. Such being the case, it cannot be allowed that Smith’s 
contributions on this particular question are really helpful. 
Apart from these considerations, a perusal of the literature convinces 
one that hitherto no one has succeeded in obtaining a really strong solution 
of the active principle of Botrytis cinerea or of any of its near allies. This 
we may conclude from the times required to bring about the various 
decompositions as recorded by the different investigators. Thus de Bary 
and Marshall Ward, in testing the action of their extracts on thin sections 
of plant tissue under the microscope, speak of a definite change being 
observable after some hours, while in the case of Behrens the action of the 
extract was allowed in some cases to proceed for twenty-four hours before 
observation was made. Now as regards the toxic action of an extract, 
it is absolutely imperative that the transformations be carried out within 
a comparatively short time. In work of this description—where the 
behaviour of living tissue is used as the indicator of a reaction—the 
complete exclusion of micro-organisms is a practical impossibility, and 
therefore observation can only be extended with confidence over the period 
during which bacterial activity is inconsiderable and while there is no 
accumulation of bacterial excretory products. How long this period may 
be will depend on various factors, prominent among which is the tempera¬ 
ture maintained ; but, speaking generally, it has been found that under 
ordinary laboratory conditions it is only with the help of special control 
measures that observation can be safely extended up to and beyond 
twenty-four hours from the commencement of the reaction. It is possible 
to extend the period of observation by lowering the temperature, a pro¬ 
cedure which greatly retards the progress of bacterial contamination, 
without retarding in anything like the same degree the activity of the 
extract. Needless to say the employment of antiseptics is not permissible 
in studies of the toxic action of an extract. 
The aim, then, of the present investigation was in the first place to 
prepare an extract from young hyphae alone, and it was hoped that 
this extract might prove to be of a sufficiently powerful nature to 
