The Neutralising Power of Calmette's Antivenomous Serum: Its Value in the Treatment of Snakebite

is poisonous because of its affinity for hoemoglobin, taking the place which oxygen occupies in the normal process of a6ration of the blood. This affinity of carbonic oxide for haemoglobin is almost exactly 300 times as great as that of oxygen. A sample of blood in a flask exposed to air containing 0.07 per cent. carbonic oxide, and shaken well up so as to absorb the gases until the heemoglobin is completely saturated, will, when examined, be found 50 per cent. saturated with oxygen and 5o per cent. saturated with carbonic oxide. Similarly, if we breathe air containing o.o6 to 0.07 per cent. carbonic oxide, the haemoglobin becomes equally satutated with oxygen and carbonic oxide. Speaking generally, the larger the percentage of carbonic oxide present in the air the higher the resulting saturation with this gas. The limit for the circulating blood is reached when its hoemoglobin is so highly saturated with carbonic oxide as to be unable to carry sufficient oxygen to support life. The first case in the series had reached the highest limit which has been observed (83 per cent.). The patient in this case had survived until only 17 per cent. of the total oxygen-carrying power of the haemoglobin was left unoccupied by the carbonic oxide. The other percentage in the cases is distinctly lower. The same variation in saturation however, is observed in the blood of coal miners who have died from the carbonic oxide resulting from an explosion in the pit.2 Since the most important point in such cases is the saturation of the haemoglobin by the carbonic oxide, it may be well to refer to the method by which it is estimated. The carmine method was first described by Haldane.3 The colour of a dilute solution of blood in the normal condition is yellow, but if carbonic oxide be combined with the heemoglobin it is pink. The intensity of the pink colour in a given sample depends on the relative proportions of carboxyhoemoglobin and oxyhaemoglobin present. It is possible by adding a dilute solution of carmine to normal blood to give it the pink colour of the blood containing carbonic oxide, and if the carmine solution be added from a burette we can measure the amount needed to give a pink of the same intensity as that due to any given saturation with carbonic oxide. As regards the pathology of the condition, two facts of importance must be kept in view. The first is the effect of the saturation of the haemoglobin with carbonic oxide is equivalent to that of depriving a person of oxygen by decreasing the amount in the air breathed. The patient poisoned by gas actually suffers from a form of suffocation. When a person exposed to carbonic oxide is found while still breathing and placed in normal air the carbonic oxide is gradually eliminated from the blood so that after some hours it has completely disappeared. The eliminating force is the affinity of the oxygen for the haemoglobin. This gradually displaces the carbonic oxide, and the higher the percentage of oxygen the quicker the elimination. The case of the child No. 5 is of importance because it is the first on record in which it was proved that in three hours practically the whole of the carbonic oxide had been eliminated from the blood. In any case, when urgent symptoms of suffocation are present, pure oxygen should be administered, or if this cannot be procured, artificial respiration should be performed. It is desirable that the patient should remain as short a time as possible under the influence of the carbonic oxide, and for this reason oxygen should be administered even when the sole advantage would be a hastening of the recovery. To the second fact-the after-effect on the patient of being nearly suffocated-I wish to call special attention, since it forms the real problem with which a physician has to deal. The more important elements of the after-effect are as follows: i. A most important effect which the deprivation of oxygen has on animals is a fall in the body temperature. This is especially true of very small animals, such as mice; it is probably also true of man. The patient, if cold, should be warmed as rapidly as possible by the ordinary means, applied externally and internally. It has been noted by Haldane that after an explosion in a coal mine the men are often observed to become unconscious or even to die suddenly when they reach the outside air. The comparative coldness of the fresh air is in all probability an important factor in producing this sudden effect. Again cases are recorded in which the temperature has risen before death, suggesting that the nerve tissues concerned in regulating' the body heat have been seriously damaged by the deprivation of oxygen. In this condition of the nervous system the effect of cold air may be greatly exaggerated. 2. When the blood is over 30 per cent. saturated with carbonic oxide even slight muscular exeicise such as walking produces violent headache, and if the saturation be a little higher the exercise unless extremely moderate causes the person to become giddy and unable to proceed. In the record of the cases Nos. 2 and 3 I mentioned that a young man in the next room had suffered from the effects of the gas, but that at first he was able to walk about and yet did not recover for over twenty-four hours. The probability is that he aggravated his condition by the exertions he made. When the blood is highly saturated with carbonic oxide treatment should include complete rest. Any exertion causes a drain on the available oxygen, and when this is much reduced the smallest additional drain is probably very serious. A most valuable account of tie effects of exertion on those poisoned by carbonic oxide will be found in the Blue Book on the Snaefell Mining Disaster. An abstract of this report was given in the BRITISH MEDICAL JOURNAL of July 2nd, 1898. 3. An increasedexcitability of the nervous system is seen in the convulsions or tetanic spasms which occur. Effects of this nature have been obtained by the partial suffocation of animals, and it is not infrequently the case that patients die from damage to the nervous system hours, or it may be days, after they have been removed from the gas. On this question interesting notes will be found in Dr. Shaw Lyttle's Appendix to Haldane's Report on Colliery Explosions, 1896. 4. The heart is frequently affected. Dr. Tomb remarks that the great source of difficulty in the case he treated (No. 5) was the condition of the heart. 5. More remote effects still have to be noted. Dr. J. R. Davison, of Belfast, described a case of gas poisoning in which the patient died after four days from pneumonia. This patient never completely recovered consciousness. Part of the general damage which the suffocation had caused was a lowering of the normal resistance to the pneumococcus.4 The fact on which all the symptoms depend is the deprivation of oxygen. The mechanism of the circulation and various nerve centres are affected because they continue in activity, during the period of suffoeation, at approximately the normal rate, while the available oxygen has been reduced to a minimum. This doubtless causes in the living tissues profound pathological changes. The nature of these changes is unknown apart from their functional manifestations.