694 
any operation whatsoever; or the effects of 
operations (resection of nerves, portions of the 
gut, ete.) could be studied after the animal 
had fully recovered. Cannon achieved this 
result by means of the X-ray. This method 
depends on the fact that food mixed with a 
salt of bismuth (subnitrate or oxychloride; an 
iron salt has also been used lately) becomes 
opaque to the X-ray. If the subject under 
investigation, man, dog, cat or other animal, 
ingests this bismuth paste, the bolus may be 
observed on the fluorescent screen, for the 
bismuth mass blocks the X-rays and betrays 
its presence to the observer by a vibrating 
shadow on this screen. The progress and 
change in shape of this shadow disclose to the 
eye of the expert observer the character of 
the muscular activity of the digestive system. 
Besides originating and perfecting this 
method Cannon has also been the foremost 
modern investigator of gastro-intestinal mo- 
tility. The experimental results with which 
he enriched physiology during the last four- 
teen years have, however, only recently been 
collected by him in a monograph, and this 
monograph is the first authoritative attempt 
to give a complete, critical study of motor di- 
gestive activities as a whole, using as a guide 
the results gained by his new method. AlI- 
though Cannon’s work forms by far the larg- 
est part of our modern knowledge of the 
motor activities of the gut, his monograph is 
by no means a one-sided presentation of the 
results obtained by his laboratory; other im- 
portant work, gained by various experimental 
methods, is critically considered and brought 
into relation with the direct testimony which 
the X-ray affords. 
The entire subject matter is considered by 
Cannon in sixteen concise chapters, and the 
chapter headings will indicate to the reader 
how completely the field has been covered. 
I., General Features of the Movements of the 
Alimentary Canal, and Methods of Investiga- 
tion; II., The Movements of Mastication and 
Deglutition; III., The Nervous Control of 
Deglutition; IV., Conditions Affecting the 
Activities of the Cardia; V., The Movements 
of the Stomach; VI., The Effect of Stomach 
SCIENCE 
[N.S. Vou. XXXV. No. 905 
Movements on the Contents; VII., The Stom- 
ach Movements in Relation to Salivary Di- 
gestion and Gastro-enterostomy; VIII., The 
Passage of Different Foodstuffs from the 
Stomach; IX., The Acid Control of the Py- 
lorus; X., The Correlating Functions of the 
Pylorus, and some Conditions Affecting It; 
XI., The Movements of the Small Intestine; 
XII., The Movements of the Large Intes- 
tine; XIII., Auscultation of Gastro-intestinal 
Sounds; XIV., The Intrinsic Innervation of 
the Gastro-intestinal Tract; XV., The Ex- 
trinsic Innervation of the Gastro-intestinal 
Tract; XVI., Depressive Nervous Influences 
Affecting Gastro-intestinal Movements. At 
the end of each chapter a complete list of the 
more important literature references is given, 
and this list will be a great convenience for 
many research workers. 
While these chapter-headings show the scope 
of the book, they give no indication of their 
interesting, and attractively presented, con- 
tents. Although it is not possible here to dis- 
cuss all the valuable and interesting sections 
of the book, and they will be found in every 
chapter, attention may be called to Cannon’s 
theory of the acid control of the pylorus. The 
pylorus, a sphincter muscle which guards the 
opening of the stomach leading to the intes- 
tine, regulates the passage of the food into 
the duodenum (upper part of the small intes- 
tine). Depending upon the character and 
state of the food in the stomach, this gate- 
keeper feeds at intervals a spurt of food into 
the gut. By what mechanism is this accom- 
plished? How ean this ring of muscle-fibers 
differentiate, for example, between carbohy- 
drates, which are permitted to leave quickly, 
and proteids, which remain for a considerable 
period of time in the stomach? 
This remarkable behavior of the pylorus 
was first explained satisfactorily by Cannon, 
and his theory, in brief, is as follows: Free 
acid above the sphincter causes a relaxation 
of the muscle ring and a peristaltic wave is 
thus able to discharge a quantity of chyme 
into the duodenum. But as soon as the chyme 
reaches the duodenum, its acidity produces a 
closure of the pylorus. The acidity of the 
