OUTGROWTH OF THE NERVE FIBER 
803 
be said that the first lymph drawn is the best; it clots readily and is 
less hemorrhagic, though this is by no means always the case. 
I^sually a single frog can be used for five or six drops. The first 
two drops were taken in most cases from the femoral sacs. After 
opening these sacs, the lymph in the crural sacs becomes so watery 
that it will not form a sufficiently firm clot for the purpose, but 
the abdominal, lateral, and dorsal sacs of the trunk, as well as 
those of the forelimb will usually each yield a small drop which 
clots firmly. The quantity obtainable from a single sac is often 
too small to be of use. In fact, whenever any very large amount 
is to be had, it is very watery in quality, as is especially the 
case in the sacs which happen to lie lowermost. This oedematous 
condition is no doubt due to weakening of the heart, action but 
oddly enough it is more pronounced in frogs which have been pithed 
than in those chloroformed. Perhaps if the auimals were anaesthe- 
tized by cold, the lymph obtained would be more uniform, and the 
low temperature would retard the clotting somewhat, which would 
be a distinct advantage. Even after taking the foregoing cir- 
cumstances into consideration it is impossible always to get 
lymph of the proper composition. It may be very thin and fail 
to clot ; or it may be so rich in fibrinogen that it clots immediately, 
even before it can be got out of the pipette, or in any case before 
the tissue can be transferred to it upon the cover. During this 
time, which is variable, some evaporation takes place and thus 
another factor of uncertainty is introduced. Still another vari- 
able is the amount of lymph relative to the amount of salt solu- 
tion taken up with the embryonic tissue. It is not surprising, 
therefore, that there should be variations in the results of the ex- 
periments, which cannot be ascribed to any particular cause. On 
the other hand it apparently makes no difference from what species 
of frog lymph is taken, Rana sylvatica, pipiens, palustris and 
clamitans, all having yielded satisfactory material. Nor does it 
seem to be of consequence that the lymph should be of the same 
species as the embryonic tissue. 
Embryos of R. sylvatica, R. pipiens, R. palustris, and, in a few 
experiments, of Bufo lentiginosus, were used, all in very nearly 
the same stage of development, corresponding to that used in most 
