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IOWA ACADEMY OF SCIENCE 
to grow, and thrive, and live to good advantage, or as Hart and 
McCollum well put it: ‘‘These results are extremely important, 
indicating what a large factor in the growth curve must lie in 
those extraneous conditions usually surrounding the animal, but 
to which m. little heed is given and concerning the details of 
which we understand so little. The salts carried by natural water 
or obtained by the animal from the soil are evidently very im- 
portant factors in promoting growth when the ration is restricted 
to the grains.’’ 
It is hardly necessary or advisable to go into greater detail 
concerning the part played by the ash, especially the mineral 
nutrients in nutrition, and the wonderful maze of factors, with 
all their possible combinations involved. The fact that in prac- 
tice progressive swine men have observed the “appetite” of the 
pig a better guide as what to supply, and how much to supply, 
and when to supply the mineral nutrients than their own “esti- 
mated mixtures” is quite to the point. In practice there is offen 
allowed such mineral feeds as limestone, (calcium carbonate pref- 
erably), charcoal, wood ashes, phosphatic rock meal (used as a 
plant food), common salt (commercial sodium chloride), cinders, 
coal screenings, sulphur, sandstone, and others, giving the swine 
free access and free-choice to these in individual trough compart- 
ments; the futility of “guessing” as to the “optimum mixture” 
for swine of all classes and ages is quite evident. 
The specific effects of various foodstuffs in changing the re- 
sistance of animals to certain poisons has been well brought out 
by Hunt^®. The specificity of different foods as regards their 
action in the , body is of great importance, and it is very essential 
indeed that the meagre information we now have concerning the 
action and reactions of the known constituents be greatly in- 
creased before we attempt to apportion out the daily food allow- 
ance over the chemical balance. There are too many unknowns 
to “play the game” of arbitrarily controlling the diet. 
There are those who suggest that swine are not intelligent, 
hence would not be very successful in “balancing their rations”. 
This is a bit beside the point but it is well to quote E-obinson^^, 
who has written very thoughtfully about the dog, horse, donkey, 
ox, sheep, goat, cat and other domestic animals. He sounds his 
28Hunt, Reid : The Effects of a Restricted Diet and of Various Diets upon 
the Resistance of Animals to Certain Poisons, Hygienic Laboratory, U. S. 
Public Health and Marine Hospital, Science Bulletin 69. See also “Experi- 
ments on the Relation of the Thyroid to Diet”, — Jour. Am. Med. Ass’n., 1911, 
LVH, 1032. 
^'-'Robinson, Louis: “Wild Traits in Tame Animals,” 1897, pp. 209-226. 
