460 SECRETION. 



entertain no doubt with regard to the glycogenic function of the liver. "We have, how- 

 ever, made some late observations which have modified our views concerning the 

 mechanism of glycogenesis ; but the fact of the production of sugar in the healthy organ- 

 ism is not affected. Notwithstanding that it seems so easy to verify these experiments, 

 there is, particularly in Great Britain, a pretty wide-spread conviction, that the liver 

 does not produce sugar during life, and that the sugar found by Bernard and others is 

 due to post-mortem action. This view is based chiefly upon the observations of Dr. Pavy, 

 of Guy's Hospital ; but it has been adopted by some authorities in Germany and in 

 France. In this state of the question, it will not be sufficient to detail merely the experi- 

 ments that seem to demonstrate the glycogenic function, but it will be necessary to exam- 

 ine these observations critically and compare them with experiments which lead, appar- 

 ently, to opposite conclusions ; for it is but fair to admit that the observations of Pavy 

 seem to be as accurate, and, at the first blush, as conclusive as those of Bernard. 



In the account of the discovery, given by Bernard, it appears that he first sought for 

 the situation in the body where the sugar derived from alimentary substances is destroyed. 

 With this end in view, he fed a dog for seven days with articles containing a large pro- 

 portion of sugar and starch. On analyzing the blood from the portal system, he found 

 a large proportion of sugar ; and he also found it in the blood of the hepatic veins. As a 

 counter-experiment, he fed a dog for seven days exclusively on meat and then looked for 

 sugar in the blood of the hepatic veins ; and, to his surprise, he found it in abundance. 

 This experiment he repeated frequently with the greatest care and always with the same 

 result ; and he concluded that sugar was formed in the liver and was contained in the 

 blood coming from this organ independently of the diet of the animal. He afterward 

 made extracts of the substance of the liver and of the other tissues, and he found that this 

 organ always contained sugar, while it was not to be detected in any other organ or tis- 

 sue in the economy. In subsequent experiments, it was demonstrated that the livers of 

 nearly all classes of animals contained sugar, and that it existed also in the human sub- 

 ject. He made observations, also, upon the mechanism of its production, its disappear- 

 ance in the blood circulating through the lungs, and the various influences which modify 

 the glycogenic function. These points will be considered in their appropriate place ; 

 and we shall now proceed, after examining the processes for the determination of sugar, 

 to take up, seriatim, the following questions : 



1. The absence of sugar from the blood of the portal system in animals that have 

 taken neither starch nor sugar into the alimentary canal. 



2. The presence of sugar in the blood as it comes directly from the liver by the 

 hepatic veins, independently of saccharine or amylaceous food. 



3. The mechanism of the production of sugar by the liver. 



Processes for the Determination of Sugar. In Bernard's first observations upon the 

 liver, he applied the fermentation-test to a simple decoction of the hepatic substance and 

 obtained unmistakable evidences of sugar. In operating upon perfectly fresh and normal 

 blood, the addition of water and subsequent filtration frequently sufficed to procure a clear 

 solution, to which the ordinary copper-tests could be applied ; but the most satisfactory 

 method of making a clear extract was to boil the blood with water and an excess of sul- 

 phate of soda. By this means a clear extract can be obtained, containing, it is true, a 

 large quantity of sulphate of soda, but this salt, fortunately, does not interfere with 

 the tests. Later, Bernard decolorized his solutions and extracts by making the liquid 

 into a paste with animal charcoal and filtering. We have long been in the habit of 

 employing both of these methods; but, when we have simply desired to determine the 

 presence or absence of sugar, the process with the sulphate of soda has proved the more 

 convenient. In delicate examinations, however, we have generally used animal char- 

 coal. We have used both methods in decolorizing the decoction of the liver-substance, 

 as well as in operating upon the blood. 



