1. Erythrocyte hemins, extracted with acid-acetone, exhibited multiple components on two chromatographic systems. However, this heterogeneity can be explained by various physicochemical properties of hemin in solution and does not imply that heme, when attached to globin in the native hemoglobin molecule, is heterogeneous. 2. The presence of a non-polar fraction may be accounted for by esterification of protohemin as a result of reaction with small amounts of methanol contaminating the acetone and/or the presence of some un-ionized protohemin molecule in solutions of low pH. 3. The presence of poorly soluble fractions is probably the result of polymerization of the hydroxyhemin molecule into so-called β- and γ-hematins. 4. The formation of mesohemin is considered unlikely, but the formation of deuterohemin or hematohemin cannot be excluded. 5. No changes in hemin chromatographic patterns were noted in disease. 6. It is necessary to evaluate reports concerning chromatographic hemin heterogeneity in the light of the artifacts described above before attributing physiologic or pathogenetic significance to the findings.

have different sensitivities to the action of tubocurarine. Investiga¬ tions have shown that the muscles of the extremities are more sensitive to curare than are the respiratory muscles.3 5 Physicians have, there¬ fore, come to equate recovery of the extremity muscle responses with full recovery of those of ventilation.Our study would indicate that this trust has not been misplaced. Several companies currently man¬ ufacture clinical nerve stimulators. These are battery-operated and rea¬ sonably inexpensive. The test for residual effects from the adminis¬ tration of curare can be carried out by anyone trained in recovery room care. The stimulators are equipped with surface electrodes, or adaptors for metal needles, that can be placed near a peripheral nerve. For convenience, we have chosen to stimulate the ulnar nerve on the medial-volar surface of the wrist.We evaluate muscle response by placing our hand in the hand of the patient, and noting the force of muscle contraction in response to single stimulations. We then ap¬ ply tetanic stimulation for five sec¬ onds, and determine whether the thumb adduction is sustained, or whether there is a rapid fatigue and a return of the thumb to the relaxed position. Finally, we again stimu¬ late with single shocks to see whether there is increased twitch tension following tetany, a phenom¬ enon termed "posttetanic facilita¬ tion."Patients exhibiting signs of fa¬ tigue from tetany and marked posttetanic facilitation signify to us the need for more anticholinesterase therapy. We first give our patients atropine sulfate in doses of 0.6 to 1.2 mg intravenously, to block the muscarinic side effects of neostigmine. Following the atropine ther¬ apy, from 1 to 5 mg of neostigmine methylsulfate is injected intrave¬ nously. The dose of this drug will depend upon the degree of the ef¬ fects resulting from the administra¬ tion of curare. In previous studies, we have determined that following twitch tension recovery to 10% of control, full recovery can usually be obtained with 2.5 mg of neostig¬ mine methylsulfate. Obviously if the state of residual effects from the administration of curare is greater, larger doses of neostigmine will be necessary to reach the end point of sustained tetanus. Because of the adverse side effects from large doses of anticholinesterases, it is our prac¬ tice not to give more than 5 mg of neostigmine methylsulfate. In the event that this is still not sufficient for antagonism, we assist the pa¬ tient's ventilation until there is spontaneous recovery.In conclusion, we feel that the use of the nerve stimulator is the best method of differentiating hypoventilation resulting from the resid¬ ual effects of the administration of curare from that of other causes. In the event that recovery room pa¬ tients show muscle weakness to nerve stimulation, either their ven¬ tilation should be assisted or they should be treated with anticholinesterase drugs. This investigation was supported in part by a grant from the Burroughs-WeJJcome Co. References 1. Katz RL: Pyridostigm...