31 
hydrocyanic acid itself, the poison produced from the nitrile.® The 
thyroid seems to alter the metabolism in such a way that the aceto- 
nitrile is disposed of without its breaking down into poisonous con- 
stituents, as occurs in the normal animal . b Were there a direct 
interaction between the poison and the thyroid the same results would 
be expected in all classes of animals; but as we shall see, thyroid not 
only does not protect rats and guinea pigs against acetonitrile, but 
it increases their susceptibility to this poison. 
The activity of the thyroid in relation to acetonitrile is in sharp 
contrast to that of certain sulphur compounds. The latter are true 
antidotes for acetonitrile as well as for many other cyanogen com- 
pounds. 0 The hydrocyanic acid which is formed from these com- 
pounds as well as hydrocyanic acid administered as such is neutralized 
by sulphur with the formation of sulphocyanate; the latter compound 
is less toxic to warm-blooded animals than the cyanogen compounds 
themselves. The action of the sulphur compounds is the same in all 
classes of animals investigated. 
An hypothesis similar to that which was advanced above to explain 
the manner in which the feeding of thyroid increases the resistance of 
mice to acetonitrile — that the thyroid simply alters metabolic pro- 
cesses in such a way that a poisonous substance is not produced from 
the nitrile- — seems sufficient to explain what is frequently called the 
detoxicatory action of the thyroid. In the normal organism the 
thyroid probably has a directing influence upon metabolism of such a 
character that all the products of metabolism are converted into 
useful or at least harmless compounds. In the absence of the thyroid 
the metabolism probably proceeds along abnormal lines, with the 
result that substances necessary for the proper functioning of certain 
organs are not formed; possibly poisonous substances are also pro- 
duced, although the evidence is against this supposition . d This 
hypothesis seems more reasonable than one assuming that poisonous 
substances are normally produced and that an organ has been evolved 
for the purpose of neutralizing them. 
« This argument is, of course, by no means conclusive. It is possible that after the 
feeding of thyroid hydrocyanic acid is produced from the nitrile, but in such a manner 
or in a place where it can be neutralized by the body, whereas when hydrocyanic acid 
itself is administered it may not reach the cells or parts of cells where neutralization 
is possible. A study of the sulphocyanate excretion of thyroid fed mice after the 
administration of acetonitrile might throw some light on this subject. 
b Another possibility which may be considered in this connection is that mice may, 
under the influence of thyroid, utilize acetonitrile for the synthesis of protein or other 
nitrogen-containing bodies. Latham (Biochem. J., 1908, 3, p. 193) believes that 
certain nitriles are utilized in this way in the normal animal. 
c See R. Hunt, Arch, internat. de pharmacodyn. e. d. ther., 1904, 12 , p. 447. 
d The blood of thyroidectomized animals is not, according to a number of writers, 
toxic; cf. L. Launoy, Semaine med., Par., 1908, 28, p. 382; D. Baldi, Arch. ital. de 
biol., Turin, 1899, 31 , p. 281. 
