464 Richards: The Effect of Chemical iRKrrATiON 



the comparativ^c violence of the irritation, reference is made to the 

 paper already cited.* It will bo seen that numerous metallic salts 

 and some organic substances were found which more or less mark- 

 edly bring about the above noted effect and that their action is con- 

 stant, although the organFc substratum, or the nitrogen source, be 

 changed. Iron salts have a double effect, noting in the first place 

 as a necessary substance for the growth of fungi, f and in the 

 second place in stronger solutions having a distinctly irritating 



effect. 



It was the object of the following recorded experiments to en- 

 deavor to throw some light on the physiological action of this 

 chemical irritation, to approach a little nearer to discovering the 

 underlying cause of the abnormal growth of these fungi under 

 such conditions. As a first step in this direction cultures and 

 analyses were made to determine if there was any regular and con- 

 siderable variation in the economic coefficient of the organic food 

 material supplied to the fungus. 



Because of its greater ease in determination sugar was employed 

 as the organic basis of the nutrient solution and many analyses 

 were made to determine what relation the weight of dry substance 

 produced for the amount of sugar used bore between the normal 

 culture, and those growing under chemical Irritation. It would, 



no doubt, hav^e been interesting for further comparison to have used 

 other organic substrata, such as glycerin, but it was hardly neccs- 

 sary in this instance to do so in order to prove the point desired, 

 and the difficulty of accurate quantitativ^e determination of glycerin 

 made it impracticable with the facilities at liand for such research. 

 For the cultures the usual method of erowinfr the fun<ri in 



^iv^rwwj^ ,.w^ ''^^'fcj 



flasks was employed. For most of the experiments the ordinary 

 Florence flasks of about 125 cc. capacity were used; they were 

 selected with due care as regards similarity of shape, and any error 

 due to difference in area of the surface of the culture fluid could 

 not have been considerable. In these flasks 50 cc. of the nu- 

 trient solution was used; for larger quantities, where 100 cc. was 

 taken, Erbenmeyer flasks of Jena glass, about 250 cc. in capacity, 



* Richards, /. c. 



f Molisch, Pflanzo in ihreii Beziehungen zum Kisen. Jena, 1892. Bcn^cke, Die zur 

 Ernflhrung der Schiuimelpilze iiothweiKlIge Metalle. Prings. Jahrb. 27 : 487. 1895. 



