WaTTERSON: EFFECT OF CHEMICAL IRRITATION 297 
the apparatus, which was measured by the size and rate of flow 
of the bubbles of air in the tubes. Any slight difference in the 
rate of flow would be of no importance when the length of time 
during which the experiment ran—six to nine days—is taken 
into consideration. Between the tubes and the aspirator were 
inserted Ba(OH), test-bottles. The aspirator was a simple one 
fastened to the water faucet. 
At the close of the experiment the aspirator was shut off, the 
stop-cocks closed, the cultures immediately killed with formalin, 
and the contents of the tubes quickly emptied into bottles which 
were tightly corked. The amount of CO, absorbed was obtained 
by titration as before. 
The metallic salts used as iets in these experiments were 
ZnSO,, FeSO, and LiCl. In each case such a concentration was 
used as had been found by Richards to be most favorable for an 
increased growth of the fungus. A 1 per cent. stock solution of 
anhydrous ZnSO, was made carefully ; of this, .3 c.c. was used 
for 75 c.c. of the nutrient solution, giving thus a .0o4 per cent. 
solution or, expressed in terms of a normal (gram equivalent) 
solution,* .00049 ; of the FeSO,, a .082 per cent. solution was 
used, or .01078 normal; and of LiCl, a .162 per cent. solution 
Or .03822 normal. 
In the following tables the results of the experiments are pre- 
sented. In the first are given five series carried on with the 
Kunstmann apparatus, for three or four days at a temperature of 
28°-31° C. The irritant was ZnSO, In the first column are 
given the dry weights of the cultures, both normal and irritated ; 
in the second the amount of CO, given off by each, expressed in 
millegrams; and in the third the ratio of the weight to the CO,. 
On examination of these figures it is evident that the addition of 
the zinc has caused an increase in the growth of the fungus and 
there has been likewise an increase in the amount of CO, respired. 
The amount of CO, respired is sometimes less than the corre- 
Sponding weight of the culture, sometimes more, but when one 
compares the ratios of the two cultures in any one series, one 
finds very little difference between them; that is, the increase in 
respiration has been | correspondingly great in both, with perhaps 
* Livingston, B. E, T The role of diffusion and osmotic pressure in plants, 22. 1903. 
