These muscular contractions which appear in mixtures of LiCl and CaCl_{2}, and do not appear in either LiCl or in CaCl_{2} alone, are not the continuation of movements caused by separating the loop from the central nervous system. These latter movements which are sometimes seen for a short time following the immersion of the loop in pure LiCl solution are inhibited by CaCl_{2}. Further, the movements which come on later in mixtures of LiCl and CaCl_{2} are of entirely different character, being convulsive and violent and many times more powerful than any movements seen in pure LiCl. If they were the movements seen in pure LiCl, only delayed by the CaCl_{2}, they should be more active in solutions containing the least CaCl_{2}. This is not the case, since in a mixture of 50 c.c. LiCl + ¹⁄₂ c.c. CaCl_{2} they are by no means so active as in 50 c.c. LiCl + 5 c.c. CaCl_{2}. A further experiment shows this still more clearly. A loop placed in 50 c.c. m/6 LiCl was allowed to come to rest, and was left in the solution for 10 minutes. No movements whatever were to be seen at this time. There were then added 5 c.c. m/6 CaCl_{2} to the LiCl solution containing the motionless loop. Within one minute the loop became violently active in the characteristic way described above. This activity continued for nearly an hour. In attempting to explain this phenomenon one is tempted to take Loeb’s suggestion as to the action of calcium in Gonionemus, namely, that it counteracts the poisonous effect of the sodium chloride. If the LiCl solution were toxic, however, it is difficult to imagine that the loop could be restored suddenly to activity as described above by the addition of a small quantity of CaCl_{2}, after it had lain in pure LiCl solution for 10 minutes. It is also difficult to consider calcium as a stimulating agent in this case, since, as shown above, in all other instances in the intestine it has the opposite action. Also calcium chloride alone in no concentration causes this phenomenon. The action of CaCl_{2} in this instance is suggestive of the action of a catalyser, the addition of which enormously hastens some chemical reaction. It is possible that the muscular activity in this case depends on a chemical reaction which is brought about neither by LiCl nor by CaCl_{2}, but by a combination of these two or perhaps by an intermediate product. Whatever may be the explanation of these phenomena, the fact remains, and is easy of demonstration, that an effect is produced on isolated loops of intestine by a combination of LiCl and CaCl_{2} which is entirely different from what can be produced by either LiCl or CaCl_{2} alone.