362 
Transactions of the Society. 
From this, “ the diffusion equilibrium has in all four cases 
been practically absolute, and it follows that all three gases can 
be diffused freely through the walls of the air bladder.” 
Here, for experimental purposes, we have the larvae subjected 
to abnormal conditions. When excessive pressures are employed 
for the purpose of demonstrating the possibility of diffusion, is it 
not conceivable that such diffusion might take place through the 
digestive track ? 
Krogh, for the sake of comparison with the compression experi- 
ments, proceeds to analyze a number of larvae from an aquarium 
constantly aerated by atmospheric air, and from eleven examina- 
tions found the nitrogen contents varied from 81 • 8 p.c. to 85 • 6 p.c.,. 
or an average of 83*5, and the oxygen contents about 16 p.c. ; in 
three cases a trace of 0 # 3 p.c. to 0’7 p.c. carbon dioxide — the bulk 
of this gas was probably lost by diffusion. This analysis gives 
results approaching the constituents of free air. 
The necessity for rapid examination is obvious, and Krogh 
states the time elapsing from the seizure of the animal until the 
bubble was ready for analysis was between 1^ to 3 minutes, and 
the analysis itself occupied 3 to 6 minutes. 
We extract the following from Arber’s “Water Plants,” which 
gives an interesting comparison between the constituents of free 
and dissolved air : — 
“ Owing to the varying solubility of atmospheric gases, the 
dissolved air differs from free air in composition. At 15° C. the 
proportions in which the constituents should occur have been 
calculated to be as under. 
“ The proportion of nitrogen given in this table naturally 
includes other inert gases which were not distinguished in Devaux’s 
time (1889). 
“ W. H. Brown (1913) suggests the excess of carbon dioxide is 
derived from the substratum being given off into the (pond) water 
from soil containing organic matter. 
We will now review the various tests and examinations that 
have been made concerning the permeability to gas or water of the 
integument of Corethra. 
1. Pupation of larva almost complete — the cast skin hanging 
from the head of larva — this we subjected to polarized light — skin 
too thin to respond, but, where folded and creased, polarized 
vividly, suggesting it is chitin, or contained some fatty substance. 
2. Transverse section of larva — shows the integument very 
lightly stained (iron hsematoxylin), excepting a thin covering on 
Free Air Dissolved Air 
“ Carbon dioxide . 
Oxygen . 
Nitrogen . 
per cent. per cent. 
0-04 2-19 
20-80 33-98 
79-16 63 - 82 ” 
