146 
MESSRS. J. N. LANGLEY AND H. M. FLETCHER 
In Experiment 9, it is clear that the fall in the percentage of salts is too slow com¬ 
pared with the fall in the rate of secretion. The probable reason of this we will 
consider with the two cases in which the percentage of salts did not follow 
Heidenhain’s law. These are— 
Table XIV. 
Eate of 
secretion 
per minute 
Percentage 
of salts. 
Weight of 
Dog 
in kilos. 
1 
Remarks. 
iu c.c. 
1 
Ex. 11. I. 
■700 
■347 I 
12i 1 
5 mgrm. pilocarpin injected be- 
II. 
■675 
■401 / 
fore I. 
Ex. 12. IX. 
1^850 
•695 •] 
r 
2 mgrm. pilocarpin injected be- 
X. 
XL 
1-650 
1-067 
■713 1 
■509 f 
151 < 
foi’e IX., 4 mgrm. before X., 
4 mgrm. before XI., 8 mgrm. 
XII. 
■950 
■543 J 
L 
before XII. 
The explanation of the variations found in experiments 9, 11, 12 we take to be that 
the pilocarpin did not bring about the normal increase in the blood flow through the 
gland. In the absence of direct observations on the blood flow in these cases, we 
cannot, of course, positively assert that the explanation we give is the true one, but 
there are certain facts somewhat in favour of it. 
In Experiment 11, the rate of secretion of organic substance is rather faster in 
II. than in I.:— 
Table XV. 
Amount of organic 
substance secreted 
ill 100 min. 
I. 
■2275 
11. 
■2322 
So that presumably the stimulus to the gland-cells either was a little stronger in II. 
than in I., or the gland had increased in irritability; but, since the rate of secretion 
of water was rather slower in II., despite this, it is probable that the blood flow 
through the gland was less in amount in II. 
In Experiment 9, the salts fall with the falling secretion, but less than normally ; 
but, since the percentage of organic substance also falls less than normally, the cause 
of the variation may be that the water is secreted less rapidly than corresponds with 
the strength of stimulus and a full blood flow; that is to say, the percentage of salts 
falls less than normally because the flow of blood through the gland falls more than 
normally. 
Lastly, we have to consider the exceptions from Heidenhain’s law in Experiment 1 2. 
If we compare the percentage of salts in IX. and XI. with that in II., we see that 
