The rates of the glycolytic processes in blood vary from animal to animal and class to class, being fairly rapid in man, dog and sheep, but slow in ox and pig.1 The important enzymes are largely present in the formed elements of the blood.2 Lundsgaard3 has shown that glycolysis is inhibited by monoiodoacetate in concentrations which do not interfere with many other enzymic processes. It is well known that glycolysis is more rapid in nitrogen than in oxygen (Pasteur reaction), probably because the oxidative and fermentative enzyme systems are competing for a compound such as methyl glyoxal, important in each type of catabolism. Accordingly it seemed possible that the Lundsgaard reagent would be more effective in inhibiting aerobic than anaerobic glycolysis, since in the latter case there is but one anti-glycolytic mechanism, in the former in a sense there are two.To test this assumption tubes were made up as follows, using blood from a single animal (dog) for each series of experiments: Defibrinated blood,...