Freudenberger (70) reported still larger thyroid 

 weights of S3 mg. for the Long-Evans strain of 

 rats, and observed significant differences between 

 the Wistar and Long-Evans strains whether 

 considered in terms of absolute value or in relation 

 to body size. The thyroid weights reported by 

 these investigators are considerably larger than 

 those reported in this publication for BHE or 

 Wistar rats. The lack of the close correlation 

 between this gland and body weight such as has 

 been reported by Donaldson (50) may be due to 

 the large weights of many of the animals, which 

 undoubtedly represent, in part at least, fat 

 deposition rather than growth of active tissues. 



Enlargement of the thyroid gland may be asso- 

 ciated with a low iodine intake. Low iodine 

 intake, however, did not appear to be responsible 

 for the enlarged glands observed with SPE diet 

 which contained 1 p.p.m. iodine. Thompson (182) 

 reported evidence that the occurrence of hyper- 

 plasia in the thyroid gland may be influenced by 

 the relative amount of iodine and calcium in the 

 diet. Differences in the relative amounts of these 

 two elements also fail to explain the differences 

 observed with diet in the size of the thyroids of 

 BHE rats. The possibility of some other mineral 

 imbalance in the diets investigated has not been 

 excluded. 



Summary. — -Diet appeared to influence the size 

 of the thyroid more than that of the adrenal gland 

 in rats that were maintaining weight when sacri- 

 ficed. The largest thyroids were found in rats fed 

 SPE diet; on SPPB diet this gland also tended to 

 be large. The influence of age on thyroid size 

 varied with the diet. Thyroid size tended to 

 parallel body weight but, as with the adrenals, 

 the correlation coefficients were relatively low. 



Thyroid size varied with age and extent of 

 weight loss as well as with diet in rats that were 

 losing weight when sacrificed. Large thyroids 

 were often associated with kidneys showing ex- 

 tensive damage. Although with some diets, 

 calcium deposition tended to parallel thyroid size, 

 possibly owing to parathyroid enlargement, cal- 

 cium deposits in the kidneys of rats fed SPPB diet 

 occurred rarely in spite of thyroid enlargement. 



The thyroid weights for moribund Wistar rats 

 fed SP 8 HVO or SPE diet were similar to those 

 for comparable BHE rats, and provide no evidence 

 for strain differences with regard to thyroid size. 



Thymus weight 



Data on the thymus weights of BHE rats were 

 obtained for a limited number of diets, and the 

 results are summarized in table 50. A marked 

 decrease occurred in the weight of this gland be- 

 tween 150 and 250 days of age regardless of the 

 diet, followed by a relatively small decrease with 

 age thereafter. Donaldson (50) reported heavier 

 thymus glands for Wistar rats of comparable age, 

 with glands weighing 211 mg. at 150 days of age 

 and 123 mg. at 250 days. 



Table 50. — Thymus weights of rats at different ages 

 on stock, SP 8 HVO, SPE, SPM, SPB, and 

 SPPB diets 



Diet and age of rats 



Rats 



Average 

 age 



Thymus weight 



(days) 



Average 



Range 



Stock : 



Less than 200 



200 to 299 



300 to 499 



500 and over 



SPSHVO: 



Less than 200 



200 to 299 



300 to 499 



500 and over 



SPE: 



Less than 200 



200 to 299 



300 to 499 



500 and over 



SPM: 



Less than 200 



200 to 299 



300 to 499 



500 and over 



SPB: 



Less than 200 



200 to 299 



300 to 499 



500 and over 



SPPB: 



Less than 200 



200 to 299_ 



300 to 499 



500 and over 



Number 



15 



11 



8 



19 



5 



7 



4 



10 



6 

 14 

 13 

 11 



5 

 5 

 5 



4 



5 

 5 

 6 



7 



5 

 5 

 2 

 9 



Days 

 148 

 258 

 454 

 586 



154 

 254 

 417 

 650 



140 

 270 

 337 

 510 



154 

 249 

 441 

 793 



154 

 250 

 426 

 633 



155 

 250 

 340 

 634 



Mg. 



106 



66 



44 



33 



151 

 65 

 69 



48 



132 



71 

 57 

 33 



118 

 58 

 49 

 44 



125 



57 

 45 

 44 



152 

 75 

 50 

 63 



Mg. 

 52-155 

 36-138 

 28- 58 

 20- 48 



100-196 

 36- 80 



41- 86 



28- 72 



92-178 

 49-101 

 22-113 

 22- 45 



64-167 

 46- 70 

 40- 72 

 25- 64 



81-164 

 38- 82 

 27- 83 

 31- 56 



78-193 

 55- 92 

 33, 66 

 45- 97 



Chemical Investigations 



Kidney 



Stock, SP 8 HVO, and SPE diets.— Data for 

 moisture, protein, fat, and ash in the kidneys from 

 rats fed stock, SP 8 HVO, and SPE diets are 

 summarized in table 51. The results for percent- 

 age composition on a dry-weight basis and for 

 total content are included. 



The data for rats maintaining weight were from 

 fasted animals except for the two age groups 

 indicated for stock rats. The results for young 

 fasted rats fed stock diet were similar to those 

 for older nonfasted rats. Neither diet nor age 

 was found to influence the composition of the 

 kidneys from these animals. Differences in con- 

 tent were related chiefly to the size of the kidney. 



Separation of the data for moribund rats was 

 on the basis of weight loss only. The results for 

 nonfasted and fasted moribund rats have been 

 combined because there was no apparent difference 

 in the composition of the kidneys from these two 

 groups of animals. The kidneys from rats that 

 had lost less than 100 grams were similar in 

 composition to the kidneys from rats that were 

 maintaining their weight at the time of sacrifice. 

 The large kidneys from rats that lost more than 

 100 grams tended to have a high percentage of 

 moisture and protein and a low percentage of fat. 



82 



