348 HUMAN PHYSIOLOGY 



Meat is peculiarly rich in extractive bodies. Among 

 these are the ones which are most surely capable of 

 arousing the gastric glands to activity. On the other 

 hand, the extractives of meat are often condemned as 

 adding needlessly to the work of the kidneys. Some 

 of them are formers of uric acid, and it is desirable in 

 many cases to keep the production of this refractory 

 waste-product at the lowest possible level. Opponents 

 of meat claim that these extractives are drug-like 

 compounds tending to establish an irritable disposition 

 and to diminish resistance to fatigue. 



The stimulating principle in tea and coffee (caffein) 

 is chemically allied to some of the extractives of meat. 

 But it does not appear to give rise to uric acid and it 

 has been shown to increase working power in a definite 

 degree. The substance theobromin in chocolate and 

 cocoa is related to caffein in composition and action but 

 is rather milder in most of its effects. It is natural 

 to suppose that any stimulant which favors a rapid 

 expenditure of energy for a time will also induce a period 

 of depression and sluggishness as a reaction. So it is 

 a surprise to learn that the most skilled investigators 

 have not detected any fall below the average normal con- 

 dition when the initial effects of caffein have passed off. 



Vitamins. The extractives we have been discussing 

 have been such as are favorable to some phases of 

 physiologic activity but not indispensable. It has 

 lately become probable that certain substances of this 

 class are truly vital in their importance that the nutri- 

 tion of the body cannot be maintained without them. 

 The name vitamin has been proposed for any such com- 

 pound, though it is probably too specific. An amin is a 

 nitrogenous body of a certain molecular type and the pre- 

 fix emphasizes the idea that the one referred to is necessary 

 to life. We do not know how many compounds there are 

 which deserve to rank as vitamins. The list will probably 

 be extended year by year. 



Deficiency Diseases. Long before the conception 

 of vitamins was clearly presented it was known that 



