162 SCIENCE PROGRESS 
observations, found that with both these organisms the CO, dis- 
charge showed an immediate and progressive diminution from 
the moment the nitrogen was substituted for air. For instance, 
three snails kept in air at 196° gave out CO, at the rate of 
322 c.c. per kilogram per hour. In nitrogen the rate of discharge 
dropped in successive half-hours to 202, 136, and 104 c.c., and 
then for the remaining five hours of the experiment to 80-90 c.c. 
Altogether 644 c.c. of CO, were given out in six and a half hours, 
whilst in another experiment at the same temperature no less 
than 1,088 c.c. were given out in the same time. These animals, 
therefore, contained a very much larger amount of separable 
CO, in their tissues than frogs do, for even at the end of these 
two experiments the CO, was still coming off at a fairly rapid 
rate. The caterpillars experimented with did not show quite so 
remarkable a result as this, but in six and a half hours at 17°5° 
they gave out CO, amounting to 446 cc. per kilogram, and 
during a further twenty-two hours they gave out 532 c.c. more, 
or 978 c.c. in all. 
In the case of warm-blooded animals it is obvious that 
exposure to an atmosphere of nitrogen would cause death and 
cessation of CO, discharge in a very few minutes. A liberation 
of CO, by the tissues does not absolutely cease, however, for 
the writer found that if an excised mammalian kidney be perfused 
with oxygenless saline it continues to give off CO, for some 
hours. This CO, rapidly dwindles down, and after an hour or 
two falls to 15-14. c.c. per hour per kilogram, but it was found 
that altogether nearly 100 c.c. per kilogram was discharged. 
The amount varied but little, whether the temperature of per- 
fusion were 15°, 20°, or 28°, just as Aubert found it to vary 
but little in the frog. Whether mammalian tissues as a whole 
contain much less separable CO, than amphibian tissues it 
is impossible to say, for it is probable that the CO, stored 
up in the different organs of an animal varies considerably, 
being, for instance, large in muscle and small in nerve. But 
at least we may conclude that it is very much larger in 
the snail than in the caterpillar, and in the caterpillar than in 
the frog. 
And by what processes is this CO, formed in the tissues in 
the absence of oxygen? Engelmann, Pfliiger, and others sup- 
pose that the protoplasm of the cells, when exposed to oxygen, 
has the power of binding it and storing it up inan intramolecular 
