466 Richards : The Effect of Chemical Irritation 



KII.PO, 

 MgSO, 



Sugar 

 Water 

 Trace of iron 



T.OO 



.50 



5.00 

 100.00 



The fungi experimented with were Sitrig^jiaiocystis (Aspcrgiilns) 

 )ihra, Pe}iicilliu})i ^laucuDi and Tnchothccuini roscuuL 



In making up the solutions it was found most convenient as well 

 as most accurate to prepare them in considerable quantities with all 

 the ingredients except the sugar and of exactly twice the strength 

 desired. Of the solutions thus prepared and with their respective 



I X 



amounts of the irritant substances added, 25 or 50 cc. were taken 

 and exactly the same amount of an accurately prepared 10^ sugar 

 solution added. , In all of the processes the same pipettes were 

 used throughout and were handled in the same manner, great care 

 being taken of course not to contaminate one solution with another, 

 particularly the control solutions. In this manner it was found 

 practicable to prepare quickly solutions containing a standard of 

 5^/ sugar with all the accuracy needed for this work. Numerous 

 test analyses were made of solutions made up after this manner 



and it was found that they did not vary more than 0.005 &^'^^^- '^^^ 

 surar content. It is obvious that it was needful to have confidence in 

 the accuracy of the solutions for upon this point depended the en- 



tire result of the work. 



When the crop of fungus was harvested the flasks were well 

 shaken and the contents filtered. To the filtrate i cc. of a 5 ^ so- 

 lution of IICI was added and time being allowed for the inversion 

 of the sugar the IICI was then neutralized with Na^CO^ and a suf- 

 ficient amount of water added to dilute the solution to just twice 

 its original bulk, thus weakening it sufficiently to allow of an ac- 

 curate analysis. From these solutions always two and sometimes 

 more analyses were made. The control cultures were usually two 

 in number ; the average between them being the figures printed in 

 the tables. The determination of the sugar was. made by the 

 Fehling method. For this purpose the usual solutions of CuSO^ 

 and of alkaline Rochelle salts were made up and mixed freshly for 

 each set of analyses. The P^ehling solution was tested against a 



