JIETAMORPHOSIS OF AXOLOXLS. 659 



The cunse of failure was probably due either to loss of potency 

 (luring process of manufacture or presence of impurities having 

 an inhibitoiy effect. As regards the first, the strength of the 

 dose was doubled with no result, so that it was not a question 

 of quantity. Tlie only impurity, apart from those accumulating 

 in process of prejiaration (a very small amount, if present), and 

 investigation of which was beyond the scope of this work, was 

 the posterior lobe of the gland. The difiiculty in separation of 

 the two lobes in dissection and diffusion of active principles 

 during dissection would account for its presence. 



It has recently been shown that there is a pigmentation factor 

 located in the posterior lobe, and by its action on the frogs' 

 melanophores a quantitative estimation can be made by deter- 

 mining that concentration which just gives a response. This 

 method .was successfully applied here and the quantity of 

 posterior lobe in each extract calculated. 



Further, many animals treated refused food, the water in the 

 container became cloudy, smelling of urine, and some eventually 

 died, after becoming greatly distended with fluid, which was 

 found to contain 2'1 per cent, of urea. As the symptoms were 

 the same in each case, and occurred only in specimens injected 

 with extracts and not controls, the cause must have been the 

 same, and introduced by the extract. Therefore the factor was 

 apparently contained in the posterior lobe and responsible for 

 inliibition of activity of anterior lobe secretion. It was possible 

 to compare roughly the amounts present by judging effects on 

 specimens. 



On comparing these observations with the results obtained 

 from the pigmentation work, the respective amounts in each 

 extract did not correspond, which seems to show that there were 

 two factoi'S at least which were not identical — the one control- 

 ling pigmentation response of the melanophores and the other 

 associated in some way with the flow of iii-ine and inhibiting 

 action of anterior lobe. It is doubtful whether the pigmentation 

 factor itself had any such action. >> 



In conclusion, it can be seen that the anteiior lobe extracts as 

 at present manufactured aie not pure, containing posterior lobe, 

 which may completely mask metamorphic action of anterior 

 lobe, although a small quantity has no effect. The varying 

 amount in which it ma}?^ be present shows consistent composition 

 and is not maintained in manufacture. Again, the stated amounts 

 of gland present in commercially prepared extracts is not to be 

 relied upon, as tested by this method. 



Piioc. ZooL. See— 192a, No. XLIII. 43 



