THE PANCREAS AND THE LIVER 119 



since its discovery and study led the celebrated 

 French physiologist, Claude Bernard, to formulate 

 for the very first time the conception of an internal 

 secretory gland. In his justly famous Legons de 

 physiologic experimentale, published as far back as 

 1855, he writes : "For a time a false conception has 

 been current as to what a secretory organ consists 

 of. It was believed that all secretions must be 

 poured upon an internal or external surface, and 

 that all secretory organs must necessarily be pro- 

 vided with an excretory duct for the purpose of 

 conveying to the exterior the products of secretion. 

 The case of the liver establishes in a most lucid 

 manner that there are internal secretions, that is, 

 secretions which, instead of being carried to the 

 exterior, are diffused directly into the blood. . . . 

 It is'now firmly established that the liver has two 

 functions of the nature of secretion. The first, 



an internal secretory gland would rule out the liver, since neither 

 glucose nor glycogen, the substances manufactured by it, can be 

 regarded as hormones. However, it has historical importance in 

 connection with Claude Bernard's work. 



If we want to stretch our definition, we could well afford to 

 include such a substance as carbon dioxide in a list of hormones. 

 It is the amount of this gas in the'blood, and not, as has been 

 supposed, the amount of oxygen, that controls the process of 

 breathing. Increased exertion, as in running, causes increased 

 production of carbon dioxide, .and this in turn stimulates more 

 rapid breathing. 



A very practical use of this new knowledge has been made by 

 Yandel Henderson, the Yale physiologist. It is only a too well 

 known fact that after anesthesia the patient's breathing is 

 poor. Professor Henderson shows -that this can b improved by 

 adding carton dioxide to the air that is administered. 



