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Studies on the Relation of Minerals to Live Weight
As these estimates are not actual values any inference from it can only be
possible on a qualified basis ; but they are capable of giving an indication of
the probable nature of the ash content. The closeness of the percentage
values under each group suggests a direct proportion with live weight.
In order, however, to work on actual values it is necessary to obtain a
sufficient number of slaughter data. Such data are generally limited, and they
are still more so in the case of bigger animals like cattle. Some data on
smaller animals were, however, available from Sherman and MacLeod's work
on rats [1925]. These have been statistically analysed by the present authors
and have formed the material for assessing the relation of calcium content of
adult animals.
The relevant points of Sherman and MacLeod's experiments are as
follows :
The animals were killed by chloroform, the alimentary tracts removed
and the bodies then ashed in silica dishes. Their previous investigation had
shown that of the total calcium in the rat's body 99 per cent was in the skeleton
and that the amount contained in the walls of the alimentary tract was entire
ly negligible so that according to them the rejection of the walls of the tract
could have ' no appreciable effect upon the determination of the total calcium
content of the body '. The entire rat minus the alimentary tract was first
charred slowly over a small flame and then ashed at a low temperature in the
muffle. The ash was dissolved in hydrochloric acid and the calcium deter
mined by McCrudden's gravimetric method [1909-10].
The rats were raised on a diet consisting essentially of a dry food mixture
of which one-third was whole milk powder and two-third ground whole wheat
or in a few cases white flour. In some cases definitely known limited amounts
of fresh meat or fresh vegetables were fed in addition, which in the quantities
here fed, were found, according to the authors ' not to influence the results so
far as concern the calcium content of the body '. Further a few of the rats
indicated by asterisks (Appendix I) had received a larger proportion of milk
powder, viz. one-half of dry food mixture and the authors state that this
increased calcium intake ' did not prove to have any appreciable effect upon
the calcium content of the animals '. The animals were all adult male rats
and their age in the majority of cases varied from 179 to 309 days while four of
them ranged from 416 to 603 days and one 849 days. The authors have given
three sets of live weights, viz. the last live weight, the net live weight and the
maximum live weight. The last live weight have been used here since they
represented the weights at the time of slaughter.
The basis of calculation has been as follows :
The calcium content of adult animals.—The estimated percentage composi
tion of ash (Table I) given by Mitchell, suggests that the ash of the body varies
directly with body weight. As calcium is a part of the ash it is also likely to
vary in a similar relation. To test this with actual data Sherman and
MacLeod's values were fitted into an equation on a power function basis. If the
value of p were near about unity it will definitely establish that the relation is
linear, if not it will deviate appreciably. The equation used was of the follow
ing order :
y=αw
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(1)