May 3, 1912] 
chyme, however, is soon neutralized by the 
alkaline bile and pancreatic juices, and then 
the free acid in the stomach produces again 
an inhibition of the sphincter tonus and 
another quantity of chyme is driven out. 
This hypothesis has been tested by Cannon 
in numerous ways. He has shown, for ex- 
ample, that anything which delays the ap- 
pearance of free acid delays the onset of the 
discharge from the stomach; that hastening 
the appearance of free acid hastens the time 
of discharge; and by means of a fistula, he was 
able to observe that the appearance of free 
acid closely precedes the first gastric discharge 
into the duodenum. In addition, Cannon 
showed that free acid causes opening of the 
pylorus in the excised stomach of a cat, thus 
proving that the control of the pylorus is in- 
dependent of the central nervous system and 
resides probably in the local nerve plexus. 
Free acid, therefore, above the gastric 
sphincter causes it to relax, and this explains 
why carbohydrates leave the stomach much 
earlier than proteids, for both these food- 
classes stimulate the secretion of gastric juice, 
as Pavlov has shown, but the proteids unite 
with the acid as it is produced, forming acid 
albumen; there is thus no free acid available 
for a considerable period of time, and, as 
shown above, free acid is necessary to cause a 
relaxation of the pylorus. There is no such 
difficulty with carbohydrates; as soon as the 
free acid appears the pylorus relaxes, and the 
crackers, potato-mush, or whatever carbohy- 
drate was fed, is at once transferred to the 
gut by the peristaltic waves of the stomach. 
The evidence that free acid below the 
sphincter, in the duodenum, causes closure of 
the pylorus, is just as conclusive, for various 
investigators had shown that acid in the duo- 
denum slows the output of chyme from the 
stomach, and this must be due to an effect on 
the pylorus, for Cannon demonstrated that 
gastric peristalsis was not stopped during 
this condition. Another support was fur- 
nished by the observation of Pavlov that acid 
solutions leave the stomach much more slowly 
in dogs with a pancreatic fistula than in nor- 
mal animals. This is easily explained by the 
SCIENCE 
695 
fact that absence of the alkaline pancreatic 
juice permits the chyme to remain acid in the 
duodenum for a longer period, and thus the 
stimulus which causes closure of the pylorus 
remains effective until the food material be- 
comes neutral or alkaline. Cannon studied 
the effects of ligation of the larger pancreatic 
and bile ducts on the rate of discharge from 
the stomach and gives a chart which shows the 
marked delay caused by this interference. 
The stimulus which causes the closure of the 
pylorus is mediated through the myenteric 
nerve plexus, for after severance of the entire 
muscular coats of the duodenum just below 
the pylorus, Cannon found that the discharge 
of the stomach content was considerably more 
rapid than in normal animals: the acid chyme 
undoubtedly still produced its usual stimulus 
in the duodenum, but this stimulus could not 
reach its destination, the pyloric sphincter, 
because its path had been destroyed. 
From the foregoing it will be seen that 
Cannon’s theory seems adequately and simply 
to explain one of the most remarkable func- 
tions in the body, and it is of theoretical in- 
terest that the same agent may exert dia- 
metrically opposite effects, the sign of this ef- 
fect being dependent upon the locus of the 
stimulation. 
It may be said, in short, that this concise 
monograph by Professor Cannon gives a bal- 
anced and authoritative view of the present 
state of our knowledge regarding the motor 
mechanism of digestion under normal and 
experimentally modified conditions. In addi- 
tion, the reader will find that the presentation 
is lucid and that dogmatic statements are ab- 
sent. 
JoHN AUER 
ROCKEFELLER INSTITUTE 
CHEMICAL TEXT-BOOKS 
The Elements of Qualitative Chemical Analy- 
sis with Special Consideration of the Appli- 
cation of the Laws of Equilibrium and of 
the Modern Theories of Solution. By 
Juuius StieeLirz, Professor of Chemistry 
in the University of Chicago. Parts I. and 
II. Fundamental Principles and their Ap- 
