INSULIN 7
Having demonstrated these facts for normal rabbits, the next thing
was to find whether insulin is capable of preventing the various forms
of hyperglycemia that are known to physiologists. Claude Bernard
was the first to show that puncture of the floor of the fourth ventricle
has the effect of causing marked glycosuria, but we found that insulin
almost entirely prevents it, as well as the hyperglycemia which is its
immediate cause. Various investigators, Stewart, Rogoff and others,
have shown that asphyxia always causes a marked hyperglycemia, but
we have found that it fails to do so in animals injected with insulin.
One form of asphyxial hyperglycemia that is quite common is that due
to poisoning by carbon monoxide. Carbon monoxide in our experience,
however, does not produce hyperglycemia after the administration of
insulin. It may cause a slight rise. Ether also fails to cause the usual
degree of hyperglycemia when it is given to rabbits injected with
insulin. This is interesting in connection with surgical operations on
diabetic patients since it must diminish the dangers due to hyper-
glycemia which are more serious in these than in normal patients. It
is of practical importance to know that insulin will diminish the degree
of ether hyperglycemia and thus diminish the risk. Another type of
hyperglycemia that is well-known to experimentalists is due to the sub-
cutaneous injection of epinephrin. In this particular case it is clear,
since you can grade the dose of epinephrin and also the amount of
insulin that is capable of presenting it, that it might be possible to
determine the dosage of insulin in terms of extent to which it can
prevent the hyperglycemia due to epinephrin.
We studied the effect of insulin on diabetic dogs in greater detail than
was possible at the time Banting and Best conducted their original
experiments. The symptoms I wish to call to your attention are:
first, the respiratory quotient, second, the glycogen metabolism, and
i third, fat metabolism. These were the three problems that Banting
and Best could not investigate while they were at the niain problem of
ascertaining whether or not it was possible to isolate a pancreatic
hormone. In regard to the respiratory quotient, you will remember
that this expresses the relationship between the amount of carbon
dioxide exhaled and the oxygen inhaled in a unit of time. It is a ratio
which tells us the kind of food that is undergoing metabolism. When
carbohydrates are undergoing combustion, the respiratory quotient is
unity; there is as much carbon dioxide given out as oxygen taken in,
for the reason that carbohydrate consists essentially of carbon plus