MAINTENANCE REQUIREMENTS OF MATTER 339 



the extent, apparently, of bringing about pathological condi- 

 tions, while on the other hand, normal feeding and conditions 

 may enable such losses, if not too extensive, to be made good. 

 The point which is of special importance is that these fluctua- 

 tions of the ash content of the skeleton affect the ash as a whole. 

 It was found by Aron that the composition of the bone ash as 

 given in Chapter II (81) remains practically constant even when 

 the skeleton has been greatly impoverished in total ash. In 

 particular this has been shown to be true not only of the calcium 

 and phosphoric acid of the bones but also of the minor in- 

 gredients such as carbonic acid, magnesium and even sodium. 

 A draft upon the skeleton for sodium, for example, could be 

 met only by the mobilization of an amount of total bone ash 

 containing the requisite quantity of sodium, and this would re- 

 sult in throwing into the circulation relatively large amounts 

 of calcium and phosphoric acid for which there may be no re- 

 quirement, thus raising the percentage of these ingredients 

 above the normal limit and leading to their excretion. 



Maintenance of ash balance 



429. Relation to feed. The foregoing paragraphs clearly 

 indicate that the ash requirements for maintenance depend 

 chiefly on the amounts of the various ash ingredients which, 

 for one reason or another, are thrown into the circulation 

 in excess of the body's needs and are therefore removed 

 by the excretory organs, and furthermore, that the nature 

 of the feed consumed, particularly the relative proportions 

 of its ash elements, is an important factor in determining these 

 losses. 



430. Deficiencies in ash ingredients. Some feeding stuffs 

 contain relatively little total ash and are especially deficient 

 in particular elements. The most striking and familiar example 

 of this is maize. According to Henry and Morrison 1 average 

 maize contains about 1.8 per cent of total ash, while its lime con- 

 tent is only 0.02 per cent and that of soda only 0.04 per cent. 

 Some by-product feeds are similarly poor in particular ingre- 

 dients. Obviously such feeds are not by themselves well adapted 



1 Feeds and Feeding, i$th Ed., p. 672. 



