268 KUNKEL: FACTORS INFLUENCING TOXICITY OF 
Quite recently Ritter (28) has made a study of the effects of 
acids on Mucors growing in several different media. He finds — 
that the toxicity of citric, malic, tartaric, hydrochloric and nitric 
acids is much reduced by the presence of peptone in the medium. 
When the source of nitrogen is ammonium citrate, ammonium 
tartrate, ammonium malate, asparagin or peptone, the toxicity of 
the various acids is much less than when the nitrogen is offered 
in the form of ammonium chloride, ammonium sulphate or 
ammonium nitrate. Grape sugar was found to saiamigly the toxicity 
of tartaric acid to a less extent than peptone. 
A review of the literature shows that the influence of the more 
complex organic compounds on toxic substances has generally 
been neglected by those who have studied the effects of poisons 
on fungi. In my further studies on this point I have tested the 
influence of carbohydrates and peptone on the toxicity of a number 
of different chlorides, and have obtained evidence which suggests 
that an important factor in toxicity is the influence of the. poison 
on the ability of the protoplast to absorb water. I have used as 
before the fungus Monilia sitophila in all of my experiments. Went 
(34) found that this fungus was able to use as a partial source 
of its food supply a rather large variety of organic compounds. 
This, together with the fact that it is a rapid grower, makes it 
especially well suited to such investigations. In experiments on 
the effects of toxic substances on fungi the choice of a standard 
by which to judge the degree of the poisonous action is a matter 
of some difficulty. One method is to grow the fungus in media 
containing the poison in different concentrations and then to 
determine the weight of the mycelium produced in the several 
media in a given period of time. On account of the difficulty 
in getting all of the mycelium out of the culture vessels and freeing 
it from constituents of the medium this method was not used. Inall 
of my experiments, I have taken as the standard for judging 
toxicity, the highest concentration of the poison in which any of the 
spores germinate after three days of incubation. The spores are 
considered to have germinated if they show any visible evidence 
of growth when magnified to about one thousand diameters. I 
find this method to be both reliable and convenient 
My cultures were grown in pint milk bottles or in two hundred 
