40) 
It follows as a logical conclusion from the 
successful effects attending its therapeutical 
use, as well as from the evil effects of its 
destruction or removal, that the thyroid 
tissue produces, normally, something that 
is in some way essential to the nutrition of 
the body. What that something is has 
been revealed partially by the beautiful 
chemical and clinical researches of Bau- 
mannand Roos. Baumann * has succeeded 
in isolating a substance, thyro-iodin, or 
iodothyrin, as it has been named more re- 
cently, which, according to the experiments 
of Roos,} preserves the beneficial effects of 
thyroid tissue. 
The chemical characteristics of this com- 
pound will doubtless be presented in Pro- 
fessor Chittenden’s paper. It has proved 
to be a very stable compound, unaffected 
by boiling, by strong acids and by gastric 
digestion, and this fact may be taken asa 
complete disproof of a former view to the ef- 
fect that the action exerted upon the body 
by thyroid tissue is due to the presence of 
special enzymes or ferments. The fact that 
extracts of thyroid tissue or iodothyrin 
when absorbed into the blood ameliorate or 
remove the evil effects resulting from loss 
of function of the thyroid, seems to prove 
at once that the normal function of thy- 
roid tissues is not merely to excrete poison- 
ous material from the blood after the man- 
ner of the kidneys. It indicates, on the 
contrary, that these tissues act normally by 
giving off a material to the blood that in 
some way affects favorably the nutrition of 
all or a part of the tissues of the body. In 
other words, the thyroid tissues form a true 
internal secretion. Histological research 
indicates that, so far as the thyroid bodies 
proper are concerned, this secretion is con- 
tained in the so-called colloidal material 
that accumulates in the interior of the vesi- 
* Baumann : Zeitschrift fiir physiolog. Chemie, Bd. 
XXI., 1896 ; also Bd. XXII. 
t+ Roos : Ibid Bd. XXII. 
SCIENCE. 
[N. S. Vou. VI. No. 132. 
cles, and that the mechanism of secretion 
consists in a rupture of the walls of the 
vesicles at some point whereby the contents 
are discharged into the surrounding lymph 
spaces.* 
The most important fact that remains to 
be discovered is the manner of action of this 
secretion upon the tissues of the body. At 
present we can only speculate upon the 
answer tothis problem. More experimental 
work is required before a definite solution 
can be reached. ‘To account for the action 
of the thyroid secretion two main hypotheses 
have been proposed. According to one 
hypothesis the function of the secretion is 
antitoxic. In some way it antagonizes an 
unknown toxic substance supposed to be 
formed in the body in the course of normal 
metabolism. When the thyroid tissues are 
removed this poisonous material, being im- 
perfectly excreted, accumulates in the blood 
and produces the fatal symptoms of thy- 
roidectomy by a process of auto-intoxi- 
cation. The other hypothesis assumes 
that the secretion of the thyroid acts 
normally by promoting or regulating the 
metabolism of other parts of the body, 
particularly, perhaps, of the nervous 
tissues. We might designate this as the 
trophic or neuro-trophic hypothesis. It is 
less specific than the antitoxie hypothesis, 
and therefore, periaps, less objectionable in 
the present incomplete state of our knowl- 
edge ; but as no decisive, or even probable, 
proof can be given for either view, it seems 
unnecessary to criticise the various facts 
brought forward in support of one or the 
other of them. The two great facts to be 
explained are: first, that complete removal 
of the thyroid tissues brings ona condition of 
malnutrition that seems to affect especially 
the central nervous system; and, second, 
that injection or ingestion of thyroid ex- 
*Biondi : Berliner klinische Wochenschrift, 1888. 
Langendorff: Archiy fiir Physiologie, 1889, Suppl. 
Bd. Schmid: Archiy fiir mik. Anatomie, 1896. 
