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poorer utilization of vegetable calcium than of milk calcium in human nutri-
tion '. They further remark (p. 45) that ' the trend of modern research is
towards the view that with the exception of sulphur, minerals in inorganic
combination are in general more readily absorbed and more completely assimi-
lated by animals than minerals in organic complexes'. Meigs and his co-
workers' investigations [1926] indicate that the calcium of carefully cured
alfalfa hay seems to be better utilized than of poorly cured hay. Turner and
his co-workers [1927] have found that the Ca and P of alfalfa hay were better
utilized than the same of clover hay while Miller's work [1926] indicates that
the Ca of clover hay is better utilized than the same of timothy hay. Some
of these investigations are not probably fully conclusive but taken all together
it may be stated without doubt that the nature and composition of the diet
exerts a profound influence on the assimilation of lime and possibly of other
minerals. The utilization of dietary calcium is, therefore, likely to be in-
fluenced by (a) the nature of the feed (b) amount and proportion of lime content,
(c) amount of food consumption (d) to some extent ratio of Ca and P and (e)
presence or absence of vitamin D.
If these be the main factors governing the utilization and absorption it will
naturally follow that the requirement in terms of absolute amount and the
requirement in relation to a particular feed may or may not be the same.
The absolute requirement may possibly be estimated by measuring the lime
excretion during a calcium free diet ; but in such circumstances there is some
probability of a compensatory attempt on the part of the system, and in
consequence the output might be depressed below the real amount. At any
rate in instances where there was a marked deficiency of calcium supply such
a tendency has been noticeable. This might possibly be obviated by adding
an integrated dose of lime compound. Here also there may be other unde-
tectable factors influencing the final output. The next course, viz. the esti-
mation of actual output in reference to the kind and quality of feeding is
therefore more convenient and has in addition the merit of practical utility.
The present paper relates to this aspect under rice straw feeding.
It is not known if any working procedure has been developed to estimate
the requirement of calcium for cattle or for other adult animals. With
reference to the requirement for human adults, however, two references can
be cited—one by Sherman [1920] and the other by Leitch [1937]. The former
used 97 observations including European and American experiments (of
which 24 were his own) and all divided between men and women subjects and
ranged from the year 1878 to 1920. The balance figures were largely negative
and he assumed that the requirement should either be the sum of intake plus
loss in the case of negative balance and intake less apparent retention in the
case of positive balance. In other words the output measured the require-
ment. The results were calculated on a uniform body weight of 70 kilos and
varied from an intake of 0.27 to 0.82 gm. Ca (average 0.45 gm.), the range
being so wide that according to his own admission [Sherman, Wheeler and
Yates, 1920] it was likely ' to throw doubt upon the average ', but it was con-
tended that ' since the average of all these experiments and the results of these
extended series are in such close agreement it seems probable that this average
of 0.45 gm. Ca per 70 kilos of body weight per day does approximately
represent the minimum maintenance requirement for normal human nutrition'.