340 Brown .— Studies in the Physiology of Parasitism. /. 
The following tables illustrate the above statements : 
/ ft \ . 
(a) In dilute concentrations (up to there is considerable agree¬ 
ment among the acids employed : the retarding effect of each increases 
gradually with the concentration. The figures represent the time in 
minutes required to produce loss of coherence in potato discs. 
Acid. 
n 
n 
00 
1024 
Citric 
20-25 
20-25 
Malic 
20-25 
20-25 
Tartaric 
20-25 
20-25 
Sulphuric 
20-25 
20-25 
Hydrochloric 
20-25 
20-25 
n 
n 
n 
n 
512 
256 
128 
64 
25 
30-35 
35 
35-40 
25 
25-30 
35 
35-40 
25 
30-35 
35 
35-40 
25 
30-35 
35-40 
40 
25-30 
30-35 
35-40 
40 
( b) In the case of sulphuric and hydrochloric acids, the retarding 
action increases very rapidly above a concentration of about —. 
n n 2n n n n n n n 
co 128 128 128 32 17 12 9 7 6 38 
H 2 S 0 4 20-22 30-35 35 35 90-105 ® 0 + + + + 
® These discs and those of the acid controls do not lose coherence within 24 hours. 
+ These discs lose coherence, the more rapidly the higher the concentration of acid; equal 
effects are shown by the acid controls. 
Hydrochloric acid shows very similar effects : thus a concentration of 
fl 
— stops the macerating action of the extract. 
1 5 
(c) The retarding action of the organic acids above the concentration 
— is much less than that of the mineral acids : 
3 ^ 
Acid. 
n 
n 
n 
n 
n 
2 n 
3 n 
4 n 
00 
160 
40 
10 
5 
T 
5 
5 
Citric 
20 
30 
40-45 
40-45 
45 
75 - 9 ° 
120-135 
210 
Malic 
20 
30 
40-45 
40-45 
45 
75 
90-105 
135-150 
Tartaric 
20 
35 
40-45 
40-45 
45 
I 35 _I 5 ° 
> 18 < 30 hrs. 
0 
® Discs do not lose coherence in 3 days. 
n 
0 
> 4 < 18 hrs. 
0 
In all these acids the retarding action is approximately equal and 
is not considerable, up to n /$; above this concentration it increases more 
rapidly. The specific retarding action is least in malic and greatest in 
tartaric acid. 
Effect of Salts and other Substances on the Activity of the Extract. 
Salts. Here, as in the case of acids, the action is one of retardation. 
The variation of the retarding effect with concentration was followed in 
detail in the case of potassium nitrate. The magnitude of the retarding 
effect will appear from the following figures, potato discs being employed. 
m 
m 
m 
m 
m 
m 
m 
m 
m 
m 
00 
572 
256 
128 
64 
32 
16 
8 
4 
2 
J 5 
15 
15 
15 + 
25 
40 
75 
180 
3|-4 hrs. 
10-20 hrs. 
J 5 
J 5 
15 
30 
45 
90 
— 
— 
