^ 402 IOWA ACADEMY OP SCIENCE 
opportunity to “telP^ what he would take; in order to grow to 
advantage. If an investigator wished to improve the methods 
of swine feeding the usual and customary procedure has been 
to use the most approved standard as a basis and compare the 
new schemes with it. The method of deductive reasoning em- 
ployed in the study of the human dietary stands in marked 
contrast to that used in the research done on swine standards. 
. The pig has been kept in the background ; whereas he might 
have occupied the foreground advantageously. 
A few closing words concerning appetite, and the factors 
affecting nutritional needs may not be amiss. Appetite is the 
resultant of thousands upon thousands of generations of bi- 
ological selection. Certain physiological specifications are in- 
herited, and then unconsciously they are fulfilled in so far as 
the environment allows. The various demands, changing from 
day to day, affect the bill of materials necessary. Every slight 
act or movement plays a specific part in creating the nutri- 
tional demands. In addition certain external factors must be 
reckoned with, such as extremes of temperature, humidity, at- 
mospheric pressure, and other conditions. 
Factors which we control and factors over which we have no 
control are operative in this business of living our lives through 
the years of development; both must be reckoned with, and 
faced squarely from the nutritive standpoint. 
SUMMARY. 
1. There is much difference of opinion as to whether or not 
the appetite may indicate reliably the nutritional needs. 
2. The futility of ideally balancing the diet or ration through 
arbitrary dietaries or standards, based on known physiological 
and chemical facts, is evident from a survey of the “field of 
possible unknowns.’^ At best the attempt will result in what 
may be considered Bough Estimates. 
3. The appetite of the pig appears to be a very good guide 
as to bodily needs ; hitherto the apparent reliability of the appe- 
tite has not been duly appreciated. 
4. Growing pigs fed sodium chloride (common salt) ad lib- 
itum made more rapid growth (increase in weight) with less 
requirement of feed per unit increase than when no salt was 
allowed, or when it was mixed in variable quantities with a basal 
ration of com grain and linseed oil meal (whole fiax grain minus 
most of the oil) . 
