306 PHYSIOLOGICAL CHEMISTRY. 



men the content is more irregular, running from 0.05 per cent 

 to 0.37 per cent. The amount seems to increase with age, but 

 no explanation for the variations can be given. In children 

 and very young animals the content is also high. It sinks, and 

 rises again, later in life. In addition to the iron a trace of 

 copper is said to be always present and may have some physio- 

 logical function. Other metals occasionally found are prob- 

 ably of accidental occurrence, as the liver retains such foreign 

 substances through a long period. 



CHEMICAL CHANGES IN THE LIVER. 



In recent years much has been written on this obscure but 

 highly important topic. Many of the changes taking place in 

 the liver come under the head of fermentations, enzymic reac- 

 tions. Hofmeister has pointed out that there are at least 

 eleven of these in play. He mentions a proteolytic and a 

 nuclein-splitting ferment, one which splits off ammonia from 

 amino acids, a rennet ferment, a fibrin ferment, an autolysing 

 ferment, a bactericidal ferment, an oxydase, a lipase, a mal- 

 tase and a glucase. We have in addition to these reactions, 

 which result in general in the breaking down of molecules, a 

 number of others which are synthetic in their nature. A brief 

 study of what is known of all these changes is sufficient to 

 indicate the immense importance of the liver in the metabolic 

 phenomena of the body. 



CARBOHYDRATE CHANGES. 



These reactions will be considered first because they have 

 been the most thoroughly studied and also because of their 

 intrinsic importance. 



Glycogen Formation. It was long ago established that 

 the food carbohydrates after digestion reach the circulation 

 almost exclusively by way of the portal vein and the liver. 

 In the normal food of man and the herbivora the carbohydrate 

 food is usually starch and this becomes dextrin, maltose and 

 finally glucose before absorption. As no marked accumula- 



