JULY 9, 1897. ] 
tracts while the animal is in this condition 
restores its metabolism more or less com- 
pletely to the normal state. While both of 
these facts are explicable in terms of either 
of the hypotheses mentioned, the trophic 
theory does not involve the somewhat 
strained assumption of an unknown toxic 
product of metabolism that can not be got 
rid of completely by the usual methods of 
excretion. 
A very interesting phase of thyroid physi- 
ology that has recently come to the front is 
the nature of the functional relationship 
between parathyroid tissue and thyroid 
tissue proper, such as is found in the thy- 
roid body and the accessory thyroids. The 
parathyroids seem to occur in all mam- 
malia. According to a recent description by 
Kohn* there is always one of these bodies 
on each side attached to the external or pos- 
terior surface of the lateral lobes of the thy- 
roid, while in some animals, e. g., the dog, 
cat and rabbit, there is an additional one on 
each side, imbedded in the substance of the 
thyroid lobes. Histologically the structure 
of these small bodies bears no resemblance 
to that of the thyroid. They possess the gen- 
eral appearance of embryological tissue, and 
have, therefore, been regarded usually as an 
immature form of thyroid tissue, which, un- 
der the stimulus of increased functional ac- 
tivity, is capable of developing into normal 
thyroid structure. Satisfactory evidence is 
lacking that such a transformation does act- 
ually take place under the conditions sup- 
posed, as, for example, after complete ex- 
cision of the two thyroid lobes. On the 
contrary, the evidence from histology, as 
well as from embryology, seems to indicate 
that the two tissues are not only funda- 
mentally different in structure, but possibly 
are also different in origin. 
On the physiological side Gley + was the 
*Kohn: Archiv fiir mik. Anatomie, Bd. 44, 1894. 
{ Gley : Archives de Physiologie normale et patho- 
logique, 1892. 
SCIENCE. 
41 
first to prove the great importance of the 
parathyroids. He showed that in rabbits 
complete extirpation of the thyroid lobes 
alone is not followed by a fatal result so 
long as the parathyroids remain. Removal 
of both thyroids and parathyroids, how- 
ever, is in most cases followed by typical 
symptoms of complete thyroidectomy end- 
ing in the death of the animal. This latter 
result has been contested by some observ- 
ers, but renewed investigations have dem- 
onstrated its accuracy. Gley explained his 
results on the hypothesis that after removal 
of the thyroid its function is vicariously 
assumed by the parathyroids. He concluded, 
therefore, that the functional value of the 
two tissues is identical. Recent work, how- 
ever, tends to throw doubt upon this con- 
clusion. Vassale and Generali* state that 
in dogs and cats removal of all four para- 
thyroids produces the acute symptoms of 
complete thyroidectomy, and finally causes 
the death of the animal, in spite of the fact 
that the thyroid body proper is left practi- 
cally uninjured. On the other hand, com- 
plete removal of the thyroid lobes is not 
immediately injurious to the animal, pro- 
vided the parathyroids—or, in some cases, if 
even only one of the parathyroids—are left. 
They contend, therefore, that the result in 
dogs and cats usually attributed to extirpa- 
tion of the thyroids is due in reality to the 
simultaneous removal of the parathyroids. 
This result is partly confirmed by the in- 
dependent experiments of Rouxeau } and of 
Gley.{ The former finds that in rabbits 
complete removal of the thyroids alone 
causes no trouble, at least no immediate 
trouble, while excision of the external para- 
thyroids alone is followed frequently by 
death, or by convulsive symptoms. Gley 
*Vassale and Generali: Archives italiennes de 
Biologie, XXV. and XXVI., 1896. 
T Rouxeau : Comptes rendus de la Soc. de Biologie, 
Jan. 9, 1897. 
{ Gley : Ibid. 
