300 SECRETION. 



mechanism of its production, its disappearance 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 will 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 saccha- 

 rine 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 on the liver, he applied the fermentation- 

 test to a simple decoction of the hepatic substance, and ob- 

 tained unmistakable evidences of sugar. In operating upon 

 perfectly fresh and normal blood, the addition of water and 

 nitration 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 sulphate of soda. 

 By this means a clear extract can be obtained, containing, it 

 is true, a large proportion 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 most convenient. In delicate examinations, 



and in persons killed suddenly while in perfect health. An opportunity lately 

 occurred in Albany for the examination of the liver in a man killed suddenly. 

 The analysis was made by the late Prof. Howard Townsend, who fully confirmed 

 the observations of Bernard (TOWNSEND, Glycogenic Function of the Liver, 

 Albany, 1864). 



