H.—3l

Effect of Goitrogenic Factor on Metabolic Rate of Rats. (b) Dr. Lawrence Malcolm (1937) has made measurements of the metabolic rate of rats on an active turnip-seed diet supplied by us, and has permitted us to summarize the results here.

Table II.

The interpretation of the results was complicated by a progressive fall in oxygen consumption during the experiments, presumably due to a deficiency in the diet. The histological examination of the thyroid glands showed in the rats on the active diet an extreme hyperplasia with many mitotic figures. The results are consistent with either of the two hypotheses : — (1) Active Brassicae seeds contain a substance with a depressant action on metabolism ; or (2) They interfere seriously with the assimilation of iodine. The thyroid hyperplasia is in each case compensatory. A direct stimulating action on the thyroid, which would entail an increase in metabolic rate, is excluded. It is proposed to repeat and extend these observations. Chapter lll.—lodine Metabolism. For the purpose of making a survey of the level of iodine metabolism throughout New Zealand, we have made use of estimations of the twenty-four-hour urinary iodine excretion. We have been indebted to outside helpers for the difficult task of collection of twenty-four-hour specimens of urine. In many cases we have been unable to secure twenty-four-hour specimens from districts we desired to study. The twenty-four-hour excretion of iodine as an index of iodine intake has the advantages that the estimation is relatively easy and that fewer analyses are necessary to establish the level of iodine metabolism than would be necessary if foodstuffs were studied. The results of all determinations are given below.

Table III. —Urinary Iodine Excretions, in Micrograms per Day: Results of All Determinations.

The median values have been given rather than the mean values, as the latter are in some cases extensively influenced by occasional high iodine excretions. These high values are attributed to the taking of medicines containing iodine or iodide, and in some cases this was verified by subsequent inquiry.

104

_ Oxygen Consumption, in Litres per Square Metre, Difference iet- per Twenty-four Hours. Per Cent. Control (steamed rape-seed) .. 191 (15 determinations) Active (turnip-seed) .. .. 174 (17 determinations) .. .. .. —8-9

(Median values are shown at foot of each column.) New Zealand. Outside New Zealand. *3 .s .§ § I a s fcf i !■§ I g 1 ja 1 flSI & a g I i a 111 ! || I ll I I I | « 2§«| ■§ 3 | I i i & g *| a s* | a g » B * 3 & II 17 21 20 23 32 10 38 21 27 30 39 47 61 55 83 80 80 13 19 27 24 27 33 24 39 25 31 37 42 63 78 70 99 82 128 18 27 30 26 39 35 27 49 37 32 45 59 63 83 72 107 114 153 22 31 34 27 41 39 27 53 42 53 56 63 71 90 74 118 119 192 23 35 37 31 43 39 32 65 46 70 57 72 77 91 91 145 120 209 23 39 37 35 45 41 32 66 51 87 58 78 79 97 107 147 121 230 23 39 41 42 45 41 33 111 61 144 65 79 80 104 114 159 173 24 46 4-1 43 77 42 37 80 285 66 88 85 122 119 165 175 24 61 42 46 80 46 41 82 76 176 98 128 135 288 182 25 119 50 54 101 51 46 97 145 267 110 170 136 613 267 27 167 59 55 123 53 47 98 155 401 161 209 168 885 29 305 78 55 155 54 48 142 228 834 687 232 894 31 82 61 64 49 32 85 63 66 58 47 97 76 85 58 48 87 93 68 58 104 70 108 78 81 83 87 87 98 110 112 914 ~24 39 46 48'5 63 53 56 61 61-5 78-5 79-5 96 110 146 147 172