1 
MESSRS. J. N. LA^fGLEY AND H. M. FLETCHER 
In this experiment, the percentage of salts follows Heidenhain’s law in all five 
cases, and does so although the slower secretions were obtained Iry stimuli so strong as 
to rapidly exhaust the irritability of the nerve, instead of by iveah stimuli. This, 
taken with Experiment 1, in which, out of six cases, there was but one exception to 
the law, and that a not very certain one, is strong confirmation of Heidenhain’s 
suggestion that the exceptions found in his experiments are due to variations in the 
rate of flow of saliva during the time of collecting any one sample. 
In all these cases, the saliva is obtained by stimulating the chorda tympani, under 
normal conditions of blood supply, except that curari or an anaesthetic in sufficient, but 
not in excessive, amount may have been given ; as we shall see later, under other con¬ 
ditions the percentage of salts does not necessarily increase with the rate of secretion 
of the saliva. Before considering what these conditions are, we may say a word or 
two about the relation between the increase of flow of saliva and the rate of increase 
of the percentage of the salts. 
Heidenhain {op. cit., p. 9) states that, with increasing rate of secretion, the per¬ 
centage of salts increases up to a maximum of '5 to ’6 per cent., so that his law really 
only holds within certain limits; when the rate of secretion passes a certain limit— 
variable in different glands—the jiercentage of salts in the saliva no longer increases. 
Wekthee, points out that the highest percentage of salts given by Heidenhain for 
sub-maxillary saliva is '66 per cent., whilst in his own experiments the maximum is 
'77 per cent. In our experiments the maximum percentage of salts is also ‘77 per cent. 
{cf. p. 122, Table VI.). Ludwig and Becher in one case found '78 per cent, of salts. 
We do not think that there is any satisfactory proof that under normal conditions 
of blood flow, and with saliva obtained by stimulating the chorda tympani, there is any 
upper limit in the rate of secretion beyond which an increase in rate no longer produces 
an increase in the percentage of salts. 
In Experiment 2, three of the samples of saliva are secreted at a fairly constant 
rate, and under similar conditions are :— 
Table 1. 
Kate of secretion 
1 
Percentage of | 
per minute in c.c. 
salts. i 
1 
TV. 
•400 
•598 
V. 
•455 
•626 
III. 
•525 
•652 
Comparing IV. and V., we see that an increase in rate of '055 c.c, a minute gives 
an increase in the percentage of salts of '028 c.c. ; the rate of increase is about '0051 
per cent, of salts for '01 c.c. a minute of saliva. 
Comparing V. and III., we see that an increase in rate of secretion of '089 c.c. a 
