310 IIEXRY A. MATTILL AXD HELEN" I. MATTILL 



nation in fasting cannot bo regarded simply as waste products from protein 

 catabolism. After 15 days Cl elimination was practically constant at 0.15 

 g. daily and was derived for the most part from disintegrated muscle sub- 

 stance. The ratio was always lower than the accepted value for 



*2^5 



flesh, 6.6, the excess of P 2 O 5 undoubtedly resulting from the metabolism 

 of bones. Elimination of S was always less than would be expected from 



the ratio -^- 13.3 in protein, and Benedict considers this an indication 



o 



of the catabolism of some substance high in nitrogen and low in sulphur. 

 The elimination of Ca and P, and to a less extent of K, in excess of that 

 accounted for by muscle catabolism may be interpreted as an indication 

 of a metabolic need for these elements which when not met by a proper 

 intake is in normal cases met by the reserves in bone. 



In their book published in 1906 Albu-Netiberg repeatedly deprecate 

 the lack of sufficiently complete metabolism experiments to enable them 

 to come to any reliable conclusions regarding the mineral requirements of 

 the adult organism. Most of the work up to that time had been limited 

 to the investigation of urinary excretion, and because of the lack of any ap- 

 proximately fixed relation between urinary and fecal output of Ca, Mg 

 or P, was valueless. They point out that only by a painstaking investiga- 

 tion not only of the urinary output but also of the fecal output and of the 

 food intake, can any reliable data regarding minimum requirements for 

 normal conditions be obtained. Furthermore, in such controlled experi- 

 ments, in which the intake is varied by the addition to the food of the 

 mineral constituents sometimes in inorganic, sometimes in organic com- 

 bination, another element of uncertainty is introduced in that the ab- 

 sorption and hence availability to the body of the minerals is not inde- 

 pendent of the form in which they are ingested, and also the absorption of 

 one -mineral constituent depends to a degree on the quantities of other 

 food materials ingested, e. g., a condition of Ca equilibrium may be con- 

 verted to a minus balance by the ingestion of an increased amount of P, 

 of carbohydrate or of fat. We have only made a beginning in the acquisi- 

 tion of data which will finally lead to as definite an understanding of 

 the mineral requirements as we now have of protein and energy require- 

 ments. With the recently attained success in feeding mixtures of puri- 

 fied foodstuffs to experimental animals has come a new method of deter- 

 mining the mineral needs. McCollum and Davis (/) have by this method 

 shown that a ration in which the acid forming elements far outweigh the 

 basic elements may support growth but is quite inadequate for reproduc- 

 tion. Osborne and Mendel (e) have varied the mineral content so as to re- 

 duce the quantity of one element after another, or of several at once, to a 

 minimum, and they find that rats grow normally and equally well whether 



