NO-VEMBER 27, 1914] 



SCIENCE 



793 



THE EFFICIENCY OF HALOGENS IN INDUCING META- 

 MOEPHOSIS IN FROG LARV^'^ 



GuDERNATSCH lias sIiowh in his interesting 

 and important experiments on the effect of 

 feeding larval frogs upon the substance of 

 certain, glands with internal secretions, that 

 thyroid accelerates metamorphosis to a marked 

 degree. Inasmuch as the present writer has 

 been studying the involution of the organs of 

 the tadpole during metamorphosis, Guder- 

 natseh's results were of significance and opened 

 at once the question as to what component of 

 the thyroid exerted this accelerating effect. 

 To the solution of this problem I turned my 

 attention during the past summer, hoping that 

 data would be found to aid in interpreting 

 the observations which have already been 

 made upon the physiological processes in- 

 volved during metamorphosis. 



Attention was first directed to the thyroid 

 constituents. All of the iodin-bearing por- 

 tions of the gland substance gave positive re- 

 sults, while the nucleoprotein, lipoid and 

 other fractions were negative. The negative 

 results given by feeding lipoid is significant 

 in the light of the theory of von Fiirth that 

 cholin is responsible for the vaso-motor ef- 

 fects of thyroid; for the lipoid-free thyroid 

 substance gave positive results, showing that 

 cholin, which is present in thyroid only in the 

 lecithins, is not functional in a vaso-motor 

 capacity in inducing the different changes in 

 the metamorphosing tadpole. Other evidence, 

 such as ligation of the chief blood-vessels of 

 the tail previous to and during involution, 

 which does not affect the rate of tissue absorp- 

 tion, points to the fact that blood changes are 

 not responsible for metamorphosis. 



lodin seems to be associated in the thyroid 

 with a globulin which Oswald has called 

 thyreoglobulin, which, on hydrolysis, is re- 

 ducible to a mass called iodothyrin by Bau- 

 mann; this is a mixture of end-products of 

 protein disintegration and especially of 

 amino-acids, some of which, such as trypto- 

 phan and tyrosin, probably hold the iodin in 

 some sort of association, but in what way is 



1 The complete details of this work are pub- 

 lished in another journal {Jour. Biol. CJiem., Vol. 

 19, 110-13). 



not known at present. Now in the present 

 set of experiments, thyreoglobulin, iodo- 

 thyrin and an iodated amino-acid, tyrosin 

 (3, 5, diodo-tyrosin), gave positive results 

 when fed separately to the larvse. The tyrosin 

 used was from a pancreatic digest and after 

 recrystallization it was iodated at 0° 0. with 

 resublimed iodin scales. 



Other iodin compounds, not derived from 

 the thyroid, were examined. Starch iodate, 

 marine iodin-bearing algae, iodated hen's egg 

 lecithin and all of the inorganic iodides tried 

 gave negative results. Iodated Witte Pep- 

 tone gave positive results, quite comparable 

 in every way with those obtained with thy- 

 roid. Inasmuch as only " organic " iodin 

 gave positive results and then only when as- 

 sociated with proteins, the conclusion seems 

 to be warranted that the iodin, in order to be 

 available, must be in some way associated with 

 amino-acids. The iodin of the plant material 

 is known not to be in the same form as in 

 thyroid, for in algse it is always associated 

 with potassium, probably as KI; therefore 

 the plant iodin is not an exception. 



Two theories may be proposed to account 

 for this effect of iodin: (1) If the process of 

 involution is due to phagocytosis as Metchni- 

 koff, Mercier and many others believe, we have 

 a basis for the accelerating action of iodin in 

 the work of Marbe, who has shown that or- 

 ganic iodin preparations raise the opsonic in- 

 dex of blood of mammals. (2) If, as the work 

 of Loss and of the present writer^ up until 

 the present time seems to show, the process con- 

 cerns, initially, at least, some factor other 

 than phagocytosis, and that probably it is a 

 matter of autolysis, then we may resort to the 

 results obtained by Kepinow, where iodin ac- 

 celerates that process. In all probability, the 

 role of iodin is two-fold, that is, instigating 

 and accelerating autolysis in the first place, 

 and secondly, favoring phagocytosis. While 

 we do not know certainly what relation exists 

 between the destructive changes, collectively 

 designated involutionary and those concerned 

 with differentiation, results obtained by the 



2Pro(i. Soc. Exp. Biol, and M" e<?.. Vol. 11, p. 184; 

 idem., Vol. 10, p. 31; Amer. Jour. Physiol., De- 

 cember, 1914. 



