22 Messrs. L. Hill and M. Greenwood, Jun. [ Oct. 1, 
Further, the observations of L. Hill and J. J. R. Macleod led them to 
conclude that all adult dogs and cats died when decompressed in a few seconds 
after an hour’s exposure (or more) to eight atmospheres. 
If the relative immunity of small animals be due to the greater velocity 
of the circulation in them, it follows that any agent which damages or slows 
the circulation would deprive them of their safeguard. We have tested 
this by exposing small animals to air pressure and then pumping chloroform 
into the chamber, or upsetting a bottle containing the anesthetic placed inside. 
8.5.07.—Guinea-pig (1 lb. 4 ozs.) placed in chamber with CHCl At 
11.30 A.M., pressure raised to + 100 lbs.; 11.35, beginning to show signs of 
ansesthesia; 12.12, decompressed from + 75 lbs. in five seconds. Dead on 
removal. P.M.: Heart auricles contained an enormous quantity of froth. 
Every vessel examined full of bubbles. Lungs almost bloodless in appear- 
ance. Renal vessels frothed on incision. Gall bladder, greatly distended, 
bile frothed almost lke soda water. 
Control 10.5.07.—Guinea-pig (1 lb. 8 ozs.) exposed to +100 Ibs. for 
30 minutes, and decompressed in seven seconds. The animal seemed normal 
on decompression, but was found dead next day (Saturday). P.M. (Monday): 
There were signs of pulmonary hemorrhage, but the body was decomposing. 
15.5.07.—Three young rats (4 ozs., 3 ozs., 2 ozs.) and a kitten were com- 
pressed at 12.50 p.m. to + 110 lbs. At 2.8, chloroform was pumped into the 
chamber, and at 2.11, when they were all lightly anzesthetised, decompres- 
sion was effected in five and a-half seconds. On opening the chamber the kitten 
and one rat were found dead. The other two rats died in a few minutes. 
P.M.: All exhibited an enormous amount of gaseous embolism except the 
rat which survived longest, and even in this case many emboli were seen, 
especially in the vena cava inferior. | 
These experiments, especially the last, are in favour of the view that 
immunity does depend on a rapid circulation. 
In considering the practical bearing of our results, 1t is to be remembered 
that the conditions which enable a small aniinal rapidly to discharge an 
excess of dissolved gas also lead to its more rapid saturation. Hence, short 
exposures are relatively more dangerous for small than large animals. 
The advantages of small body mass and youth should accordingly be more 
apparent among caisson workers than in diving operations; we are not 
acquainted with any statistics bearing on this point. 
It is interesting to note that we have no reason to think that small 
animals are more susceptible to oxygen poisoning than large ones. The 
following observations of L. Hill, J. J. R. Macleod, and C. Ham are suggestive 
of this :— 
