INFLUENCE OF THYMUS FEEDING UPON DEVELOPMENT 147 
larvae failed to show that the thymus had exerted any growth- 
accelerating influence. On the other hand, the quantity of food 
given plays an important part in this connection, for the animals 
react in a highly sensitive manner to relatively slight differences 
in'food quantities. From these experiments it would seem that 
in the experiments on tadpoles conducted by Gudernatsch and 
Romeis the factor revealed is not a specifically growth-promoting 
influence, but that the accelerated growth of the thymus animals 
should be attributed to the fact that the jaws of the tadpoles, 
although adequate to supply the body with a quantity of the 
soft thymus material corresponding to the needs of the organism, 
were nevertheless not the most appropriate instrument for pre- 
paring from the hard beef muscle sufficient nutriment for the 
purpose of keeping up normal growth. The very fluctuating 
results which Romeis obtained in his experiments indicate pro- 
nounced sensitiveness on the part of the tadpoles to small quanti- 
tative differences of food which often completely escape control, 
rather than the presence in the thymus of a specific growth- 
promoting influence. It should also be remarked that in the 
above-mentioned experimental group it was also noted that the 
animals fed with worms must consume a much greater quantity 
of earth-worms than the thymus-fed animals consume of thy- 
mus in order to grow equally quickly; the supply of earth-worm 
fragments which the second series consumed was only slightly 
smaller than that of the first series fed with fragments of thymus. 
This fact speaks in favor of relatively high nutritive value in the 
thymus. It should also be taken into consideration that in the 
fragments of earth-worms a not inconsiderable part of the volume 
consumed consists of indigestible substance (chitin, earth) which 
are later eliminated in the feces. 
In the preceding order of experimentation it is seen that at the 
moment that the tetany period begins in the thymus-fed animals 
we are confronted by an obstacle which prevents any quantitative 
judgment from being formed; for from this time on the thymus 
animals are seen to be abnormally placed and the amount of 
food taken in by them becomes abnormally low. This is all 
the more disturbing for the reason that it is uncertain whether 
