In the course of an experimental investigation into the effects of varying diets on the structure and function of the tissues in tame rats, my attention has incidentally been directed to the various glands in wild rats. On post-mortem examination of wild rats it was found that the adrenal glands in these animals were considerably larger than in tame rats of similar weights. The explanation which suggests itself as the most likely one has reference to the greater muscular activity in wild rats, the changed diet of the animals may also be a factor. As the data so far obtained are of interest, and suggest a somewhat new line of inquiry as to the influence of different environmental conditions on the structure and functions of organs, I think it well to record the facts given in the following tables. The adrenal glands were in every instance weighed out of a 5 per cent, solution of formalin, the excess of fluid being previously removed.

Table I. gives the percentage weight of the adrenal tissue in twenty-seven young tame rats, none of the animals being fully grown. Of these, eighteen were under 100 grammes, and nine weighed from 100 to 150 grammes. Table II. gives the percentage weight in nineteen fully grown tame rats. The average percentage weight is as follows: -

For the young animals under 100 grammes in weight

0.35 gramme.

For the young animals not fully grown

.023 "

For the full-grown adult......

.019 "

To turn to the wild rats, we find the facts recorded in Tables III. and IV.

1 Chalmers Watson, Journal of Physiology, 1907.

Table I - Showing Percentage Weight Of Adrenal Glands In Young Rats (Tame)

Weight of Animal.

Weight of Glands

We

52 grms.

.022 grm.

•042 grm

57 "

•020 ,,

•034 "

60 „

•020 „

..

60 ,,

.024 .,

.040 "

60 „

.026 ,,

•043 ,,

65 "

.028 „

•043 "

69 „

.030 "

•043 "

72 .,

•02; .,

.031 ..

73 ..

..

..

77 "

026 „

•035 "

77 „

■024 ,.

.032 "

77 ..

•024 „

.032 "

80 „

028

•035 ..

84 „

•030 „

•035 "

87 "

•024 ,,

.027 ,,

87 ..

•020 ,,

•029 „

95 "

.029 „

•030 ,,

99 "

•034 "

•034 „

Average

•035 "

110 grms.

•032 grm.

•029 grm.

115 "

•02; ,.

•020 .,

120 „

•024 „

•020 ,,

120 ,.

•039 ..

•015 "

140 .,

•044 .,

•031 .,

150 „

•042 „

•028 „

150 ".

•040 „

•026 ,,

150 „

•030 „

•020 ,,

150 „

•028 ,,

•018 ,,

Average

•023 "

Table II. Showing Weight Of Adrenal Glands In Fully-Rown Tame Rats

Weight of

Animal.

Weight of

Two Glands.

Percentage Weight.

110 grms.

•028 grm.

026 grm.

115 "

035 "

•030 „

120 „

•035 "

•029 „

145 "

•026 ,,

•018 „

160 „

•040 ,.

•025 „

165 ..

•032 „

•019 „

170 „

•024 „

•014 ..

182 „

•034 .,

•018 ,.

185 "

•040 „

•021 „

195 ..

•040 „

020 „

210 „

035 "

•014 "

..

.039 "

.016 „

240 ,.

.033 "

•0I3 ,,

.

.009 "

•027 „

265 "

..

•015 .,

285 "

.065 „

•022 „

300 „

•034 ,,

•018 ,,

310 „

.050 ,.

•016 „

310 „

•058 „

•018 „

Average

•019 ..

Table III. Showing Weight Of Adrenal Glands In Young Rats (Wild)

Weight of Animal.

Weight of Two Glands.

Percentage Weight.

60 grms.

•037 grm

•061 grm.

,.

•040 ,,

.058 „

72 „

.044 ..

•061 „

72 „

■044 ..

•061 „

75 ,,

•050 „

•066 „

76 "

.041 .,

•053 „

80 „

•074 "

.092 ,,

83 .,

.085 „

• 102

85 ,,

.069 "

•082 ,,

86 „

•059 "

•067 ,,

92 „

•058 "

•063 "

95 "

•052 "

•054 ,.

96 "

•048 „

•050 ,.

98 „

•058 „

•059 .,

100 „

•060 ,,

.060 „

Average

.066 „

102 grms.

.068 grm.

•066 grm.

106 ..

•065 ,,

•061 „

110 ,,

•054 ..

.049 ,.

130 „

•116 „

•089 „

130 „

•160 ,,

• 122 ,,

140 „

•130 "

.092 ,,

142 „

•095 .,

•066 ..

Average

•077 "

Table IV. Showing Weight Of Adrenal Glands In Fully -Grown Wild Rats

Weight of

Animal.

Weight of Glands.

Percentage Weight.

I 50 grms.

.085 grm.

•056 gnn.

190 ,.

•125 „

•065 „

I90 „

•105 „

•055 .,

200 „

•123 .,

•061 „

207 „

•093 "

•044 "

220 „

•093 "

•042 „

237 "

•108 „

•049 ..

240 "

•135 ..

.056 „

242 ,.

• 162 „

•066 ,,

260 „

.165 ..

•063 „

260 ,.

•220 „

.084 „

260 ,.

.114 .,

•043 "

270 „

• 134 ..

•049 .,

305 „

•120 "

•039 "

340 "

•170 ,.

•050 „

342 „

.129 „

•037 „

370 „

•128 ,,

034 „

Average

•052 „

In fifteen wild rats under 100 grammes in weight the aver.: percentage weight of the adrenal tissue was 066 gramme as opposed to •035 gramme in the tame animals; in seven young animals not fully grown, between 100 and 150 grammes in weight, the average was 077 gramme as opposed to .023 gramme in the corresponding series of tame rats; in seventeen wild rats that were assumed to be fully grown, the average percentage weight of the glands was .052 gramme as opposed to .019 in the case of the fully-grown tame subjects.

The two noteworthy facts to which attention is directed are: -

(1) The greater amount of adrenal tissue in wild rats in comparison with tame rats of equal weight.

(2) In wild rats there is not the same disproportion in the amount of adrenal tissue in the young and adult subject as obtains in the tame rat.