226 



NA TURE 



[January 9, 1908 



states that the fragments of sandstone, shale, &c., 

 that he has found enclosed in the blue ground are 

 conspicuously unaltered. 



Much of the recent controversy has centred round 

 the relation of the kimberlite dykes to the pipes. The 

 fact that material of practically identical character to 

 the pipe rock, and similarly brecciated, occurs in the 

 form of dykes has long been known; but the latter 

 have hitherto attracted but little attention, owing to 

 the fact that the dyke material either carries no dia- 

 monds or so few as to be unworkable at a profit. 



There can be no doubt that the dykes are genetically 

 connected with the pipes, but were they formed con- 

 temporaneously, or did the dykes precede the pipes or 

 vice versA? Dr. Voit states that the pipes are younger 

 than the dykes, which in all cases terminate, according 

 to him, at the pipe-walls. Besides, fragments of dyke 

 rock occur in the pipes, but pipe rock is never found 

 in the dykes. Although chemically identical magmas, 

 there are slight mineralogical distinctions, due, prob- 

 ably, to the different rate of cooling, which enable the 

 rocks to be easily identified. Du Toit advocates the 

 contrary view, namely, that the pipes and fissures have 

 been formed contemporaneously. Between the ex- 

 tremes of occurrence in pipes or dykes he traces every 

 gradation, and mentions "fissure-swellings," which, 

 though dyke-like, expand at one or more points. 

 Almost every pipe will be found to have one or more 

 dyke-like offshoots, if not at the surface, at some 

 greater depth. In the Newlands group, the pipes are 

 connected below ground by a narrow dyke of kim- 

 berlite ; on Secretaris, west of Kimberley, there are 

 fissures with one or more little swellings on them, 

 and there are numerous dykes and veins varying in 

 width from mere stringers to belts of many feet. The 

 strike of the fissures corresponds in some instances 

 to that of the enclosing rocks (Newlands, Smith, and 

 Peiser mines), indicating that the intrusion followed 

 planes of physical weakness. 



Instances might be multiplied to show the differ- 

 ences of opinion that obtain among South African 

 geologists with regard to these interesting occur- 

 rences. They only emphasise the difficulties of the 

 pioblems awaiting solution. 



One word as to the date of intrusion. The pipes 

 and fissures are later than the Karroo dolerites, which, 

 in their turn, cut the Stormberg lavas. They are 

 therefore at least of post-Rheetic age. If the melilite- 

 basalt pipes of Suthei-land are connected in origin 

 with an intrusion of melilite-basalt in the Uitenhage 

 beds at Spiegel River (Heidelberg, Cape Colony), then 

 the occurrences of kimberlite are of post-Neocomian 

 age {vide Rogers and du Toit, loc. cit.). 



F. H. Hatch. 



THE INDUCTION OF ANESTHESIA BY 

 CHLOROFORM. 



THE inquiry which was initiated seven years ago 

 by the Council of the British Medical Associa- 

 ation into the man5'-sided problem of chloroform- 

 anaesthesia has added greatly to our knowledge, and 

 directed particular attention to the fact that the ad- 

 ministration of an amount of chloroform vapour above 

 2 per cent, in the inspired air is fraught with danger 

 to the patient. The scope cif this inquiry has been 

 further supplemented and extended by independent 

 researches carried out in this country and in France. 

 The view has been held, and to some extent 

 verified by experiments, that during the progress of 

 anaesthesia the drug was absorbed by the corpuscles 

 rather than by the plasma of blood. The experiments 

 of Benjamin ' Moore and H. E. Roaf first definitely 

 proved that in vitro, with an adequate concentration or 



NO. 1993, VOL. 77] 



solution tension of chloroform in the blood, easily 

 dissociable compounds or aggregations were formed 

 between the drug and the proteins, including haemo- 

 globin, of the blood. It was a natural inference from 

 these experiments that the production of anaesthesia, 

 either in isolated cells or in unicellular or multicellular 

 organisms, was due to the formation of such com- 

 pounds between cell-protoplasm and chloroform. With 

 a very small constant quantity of chloroform, i per 

 100,000, in blood it has been found that the anaesthetic 

 effect is in no sense a cumulative one ; the degree to 

 which a living tissue is affected depends entirely upon 

 the concentration of the chloroform in the blood, and 

 therefore in the living cell, for the degree of anaes- 

 thesia remains constant, and persists for only so long 

 as a definite solution pressure is maintained. Any 

 given grade of anaesthesia is therefore entirely inde- 

 pendent of the total amount of chloroform which is 

 supplied at an adequate concentration. In the induc- 

 tion of anaesthesia in man the various stages from 

 slight to profound must therefore essentially depend 

 upon the gradually rising pressure of chloroform in the 

 blood. When the amount of chloroform in inspired 

 air is very low, the induction of anaesthesia is im- 

 possible; while that too high a percentage is lethal, the 

 unfortunate accidents which occur from time to time 

 bear abundant witness. 



The rate of absorption of chloroform during the 

 induction of ansesthesia has been studied by many 

 observers, most of whom have attempted a solution of 

 this problem by ascertaining the degree to which 

 the lungs are ventilated during narcosis, and the ex- 

 tent to which chloroform is apparently retained by 

 the body. This is determined by estimating the 

 difference between the chloroform-content of inspired 

 and expired air. In the case of inspired air this can 

 easily be done with accuracy, but, especially with a 

 low percentage of chloroform, the corrections which 

 are necessary for temperature, amount of carbon- 

 dioxide and aqueous vapour are so great as to render 

 an accurate determination of the amount of chloroform 

 in expired air a matter of much difficulty. 



The rate at which chloroform is taken up by the 

 blood can, however, be directly measured. In three 

 papers just published in the Proceedings of the Royal 

 Society, Dr. G. A. Buckmaster and Mr. J. A. 

 Gardner have described the exact procedure of their 

 experiments, which were undertaken with the view 

 of ascertaining the function of the red corpuscles in 

 anaesthesia produced by chloroform. Two of the 

 papers fully describe experimental studies on " The 

 rate of the assumption of chloroform by the blood 

 during anaesthesia," and " The rate of elimination of 

 chloroform from the blood after anaesthesia." 



Hitherto an exact determination of chloroform in 

 blood has been found to be difficult. It is not possible 

 to use Neumann's method for chlorides. French 

 observers, Tissot, Mansion, and Nicloux, have em- 

 ployed a method which is based on Dumas's reaction, 

 which, as carried out by Nicloux, is rapid, convenient, 

 and capable of giving satisfactory results, though 

 it does not possess such a high degree of precision 

 as an exact chemical method as does the one which 

 was introduced by Carius for the determination 

 of chlorine in organic compounds. This method 

 was first used by Buckmaster and Gardner in _ their 

 experiments on the anaesthetic and lethal quantity of 

 chloroform in blood. The maximum error of this 

 method never exceeds five per cent., and is generally 

 much less. The amount of chloroform in the blood 

 at any stage of anaesthesia is calculated from the 

 difference between the chlorine-content of the blood 

 of each individual animal before and after the induc- 

 tion of anaesthesia. 



