CHEMISTRY OF DIGESTION AND NUTRITION. 357 



case of the dog he obtained the following results (mineral constituents in 

 100 parts of ash) : 



Young Pup. Dog's Milk. Dog's Serum. 



K 2 8.5 10.7 2.4 



Na 2 8.2 6.1 52.1 



CaO 35.8 34.4 2.1 



MgO 1.6 1.5 0.5 



F 2 3 0.34 0.14 0.12 



P 2 5 39.8 37.5 5.9 



CI 7.3 12.4 47.6 



The remarkable quantitative resemblance between the ash of milk and the 

 ash of the body of the young indicates that the inorganic constituents of milk 

 are especially adapted to the needs of the young; while the equally striking 

 difference between the ash of milk and the ash of the maternal blood seems to 

 show that the inorganic salts of milk are formed from the blood-serum not 

 simply by diffusion, but rather by some selective secretory act. These facts 

 come out most markedly in connection with the CaO and the P 2 5 . For 

 further details as to the history of calcium and iron in the body, consult the 

 section on Chemistry of the Body, under calcium and iron. 



I. Accessory Articles of Diet ; Variations of Body-metabolism 

 under Different Conditions ; Potential Energy of Food ; 

 Dietetics. 

 Accessory Articles of Diet. — By accessory articles of diet we mean those 

 substances that are taken with food, not for the purpose of replacing tissue or 

 yielding energy, but to add to the enjoyment of eating, to stimulate the appetite, 

 to aid in digestion and absorption, or for some other subsidiary purpose. They 

 include such things as the condiments (mustard, pepper, etc.), the flavors, and 

 the stimulants (alcohol, coffee, tea, chocolate, beef-extracts). They all possess, 

 undoubtedly, a positive nutritive or digestive value beyond contributing to the 

 mere pleasures of the palate, but their importance is of a subordinate character 

 as compared with the so-called alimentary principles. They may be omitted 

 from the diet, as happens or may happen in the ease of animals, without 

 affecting injuriously the nutrition of the body, although it is probable tli.it 

 neither man nor the lower animals would voluntarily eat food entirely devoid 

 of flavor. 



Stimulants. — The well-known stimulating effect of alcohol, tea, coffee, etc., is 

 generally attributed to a specific action on the nervous system whereby the irri- 

 tability of the tissue is increased. The physiological effect of tea, coffee, and 

 chocolate is due to the alkaloids callein (triinetliyl-xanthin) and thcobromin 

 (dimethyl-xanthin). In small doses these substances are oxidized in the 

 body and yield a corresponding amount of energy, but their value from this 

 standpoint is altogether unimportant compared with their act ion as stimulants. 

 Alcohol also, when not taken in too large quantities, may be oxidized in the 

 body and furnish a not inconsiderable amount of energy. It is, however, a 

 matter of controversy at present whether alcohol in small doses can be con- 



