374 
AGRICULTURE: HART, AND OTHERS 
ably led to too low results and it is significant that those so obtained were lower than those 
obtained when iodometric methods were used. See 'The lodometric Determination of Sul- 
fur Dioxide and the Sulfites,' J. B. Ferguson, /. Amer. Chem. Soc, Easton, Pa., 39, 1917, 
(364). 
^ Thomsen's value is 71080. (Thomsen, Thermische Untersuchungen, 2, p. 251) 
^ This value agrees with that derived from some preliminary investigations by M. Ran- 
dall on sulfur and water {Thesis, Mass. Inst. Tech., Boston, 1912) and also with that ob- 
tained by Lewis and Bichowsky in a more complete investigation carried out at higher tem- 
peratures (private communication). 
PHYSIOLOGICAL EFFECT ON GROWTH AND REPRODUCTION OF 
RATIONS BALANCED FROM RESTRICTED SOURCES 
By E. B. Hart, E. V. McCollum, H. Steenbock, and G. C. Humphrey 
DEPARTMENTS OF AGRICULTURAL CHEMISTRY AND ANIMAL HUSBANDRY. UNIVERSITY 
OF WISCONSIN. MADISON 
Communicated by R. Pearl. March 29, 1917 
Our early work^ on the nutrition of herbivora with restricted rations 
demonstrated clearly the inadequacy of the accepted theory as to what 
constitutes a balanced or complete ration. Up to that time total pro- 
tein — without reference to quality — energy, and ash materials were 
considered the essentials of a ration. The latter, however, occupied no 
position in the mathematical expression of the standards developed. 
The standards have been stated only in terms of total digestible pro- 
tein and energy. It is, however, probably true that in a practical sense, 
and with the generally accepted knowledge of the quality of materials 
accumulated from a long and varied experience, that such standards 
have had and will continue to have very great value ; but their limita- 
tions are also made evident by this earlier work and are emphasized by 
what we have since done. Within the past few years our knowledge^ 
of the essentials of a ration have expanded and today we would consider 
a ration complete and efficient only when it contained protein of ade- 
quate quantity and quality, adequate energy, ash materials in proper 
quantity and proportion and two factors of unknown constitution 
(vitamines), designated from this laboratory^ fat soluble A and water 
soluble B. 
In addition to the above normal factors there may be introduced 
with natural food-stuffs the important factor of toxicity.^ This can be 
wholly absent or so mild in its effects as to be entirely obscured when 
the other essentials of a ration are at an optimum adjustment; or with 
fair adjustment it may only reveal its effects when the ration is con- 
tinued over a very long time and the animal involved in the extra 
strains of reproduction and milk secretion. This resistance to toxicity 
