458 



NA TURE 



[February i8, 1909 



As it is a difficult matter to purify completely the small 

 volume of emanation and to keep it pure, the observed 

 pressure of the emanation and mixed gases at the tempera- 

 ture of condensation was corrected for by taking the true 

 volume of the emanation from i gram of radium in 

 equilibrium as 0585 cubic milligram. This calculated 

 volume is in excellent agrcctrient with the minimum value 

 which I have found experimentally. .'\s the emanation is 

 apparently an inert gas of atomic weight 222, it is of 

 interest to compare its boiling point with those of the 

 heavier inert gases found in the atmosphere. The boiling 

 points of argon, krypton, xenon, and emanation are, re- 

 spectively, 86-9, I2I-3, 163-9, =i"<l 208 degrees absolute. It 

 will be noted that as the boiling point of krypton is about 

 intermediate between that of argon and xenon, so the boil- 

 ing point of xenon is nearly the mean between that of 

 krypton and emanation. 



If the capillary tube containing pure emanation is quickly 

 placed in the pcntane bath, cooled well below the tempera- 

 fure of initial condensation, under a microscope small drops 

 of liquid emanation are seen on the walls of the capillary. 

 The position of each globule is marked by a brilliant local 

 phosphorescence of the glass of the capillary. 



E. Rutherford. 



University, Manchester, February 13. 



Crocodiles and Tsetse-flies. 



Mv attention has been directed to a paper read before 

 the Royal Society of Arts by Mr. James Cantlie on 

 January 27 called " The Part played by Vermin in the 

 .Spread of Disease," published in the society's journal 

 (January 29, pp. 202-4). Mr. Cantlie is there reported to 

 have said: — "In sleeping sickness the disease is trans- 

 mitted by the tsetse-fly, and the crocodile is believed to be 

 the alternative host, the fly serving as a carrier only " 

 (p. 204). 



I do not know upon what evidence or upon whose 

 observations Mr. Cantlie based his statement concerning 

 the crocodile, but to judge from many similar statements 

 that have appeared from time to time recently in the Press, 

 the idea seems to be generally prevalent that Prof. Koch 

 cither observed or believed that the crocodile was a 

 " reservoir " host for the human trypanosome (Trypano- 

 soma gambieiise), just as big game is for the trvpariosomc 

 causing^ the " nagana " disease of animals (t. brucei). 

 Prof. Koch, however, has never expressed such a view in 

 his published papers. In his last work on this subject, 

 " Uber meine Schlafkrankheits-Expedition " (Berlin : 

 Dietrich Reimer, 1908), he wrote : — " Dem ersten . . . 

 Krokodil cntnahmen wir sofort frisches Blut, um Priiparate 

 7u machen und Kulturen anzulegcn, und wir batten in 

 diesem Falle auch insofern Gliick, als die Kulturen 

 gelangen, wodurch wichtige wissenschaftliche Resultate 

 erhalten w^urden. Xamentlich konnte auch festgestellt 

 werden, dass das Blut des Krokodiles zwar Trypanosomcn, 

 aber tiicht diejenigen der Schlafkrankheit cnthiilt " (the 

 italics are mine). 



All that Prof. Koch showed was that the crocodile in 

 the Victoria Nyanza is infected by a species of trypano- 

 some, and that tsetse-flies (Glossiiia palpalis) feed on the 

 blood of the crocodile. Both these facts had already been 

 made known by English observers. The bare fact that the 

 crocodile may be infected by trypanosomes is no evidence 

 for connecting this reptile with sleeping sickness. The 

 perch, bream, tench, and other fishes in the Norfolk Broads 

 also commonly harbour trypanosomes in their blood, but 

 are not to be regarded as a danger to mankind on that 

 account. There is, in fact, no evidence whatever that the 

 crocodile serves as an " alternative host " of the human 

 trypanosome. It is inherently improbable that any reptile 

 should play such a part. 



I hold no brief for the crocodile, and should hear of its 

 extirpation in the Victoria Nyanza without the least regret ; 

 1_ only desire that our scientific knowledge of the sleeping- 

 sickness trypanosome should be correctly stated. It is 

 possible, and indeed for many reasons probable, that a 

 •' reservoir " host for T. gambicnse exists, but none has 



NO. 2051, VOL. 79] 



been discovered as vet. Only the human species has been 

 found so far to be naturally infected with the trypanosome 

 of sleeping sickness, although many other mammals can 

 be inoculated with it as a laboratory experiment. 



Rovigno, February 10. E. A. Minchix. 



The Production of Prolonged Apncea in Man. 



It is a matter of common knowledge that the time for 

 which the breath can be held is increased by a preliminary 

 bout of deep breathing, and divers often make use of this 

 fact to increase the time for which they can remain under 

 water. So far as I am aware, it is not usual to perform 

 this forcible respiration for more than a short period, the 

 pearl-divers of Ceylon, for instance, taking only a few 

 deep breaths before descending ; but in order to get the 

 maximum effect a prolonged period is necessary. In my 

 own case I found that whilst with no preliminary forced 

 breathing I could hold my breath for only forty-two 

 seconds, I could hold it for 2m. 21s. after one minute's 

 forced breathing, for 3m. 21s. after three minutes' breath- 

 ing, and for 4m. 5s. after six minutes' breathing {c.f 

 Journ. Physiol., vol. xxxviii.). The effect of the forced 

 breathing is to wash out such considerable quantities of 

 carbon dioxide from the blood and body tissues that even 

 at the end of the three or four minutes' apnoea they con- 

 lain less of the gas than when the breath is held for forly- 

 two seconds without any preliminary forced breathing. 



In theory, therefore, the deeper, more rapid, and more 

 prolonged the forced respiration the greater its efficacy ; 

 but it is not so in practice. With some people the sensa- 

 tions produced by even a minute or two of forced breath- 

 ing are very unpleasant. The hands and feet tingle and 

 become numb, a dizziness is felt, and there is a strong 

 disinclination to continue the breathing {_cj. Haldane and 

 I'oulton, joinn. Physiol., vol. xxxvii.). In my own case 

 a period of eight minutes' breathing caused the muscles 

 of the hands to pass into a condition of tonic rigidity, and 

 they remained completely paralysed for the first ij minutes 

 of the subsequent apncea. Doubtless the unpleasant sensa- 

 tions are diminished by practice, but it is probable that 

 for ordinary purposes it would be best not to continue the 

 forced breathing for more than two or three minutes. Also 

 there is a distinct element of risk if a diver remains under 

 water almost to his limit after forced respiration. The 

 amount of oxygen left in the lungs and blood then become- 

 so low that there is danger of fainting. Haldane and 

 Poullon quote a case, of which they were informed by 

 Dr. Collier, in which a diver lost consciousness when at 

 the bottom of a swimming-bath after he had employed 

 forced breathing to prolong his stay under water. Fortu- 

 nately, he was rescued before death occurred, but un- 

 doubtedly the chance of fatality is increased by a pre- 

 liminary forced respiration. 



In the absence of forced breathing, the accumulation of 

 carbon dioxide in the blood when the breath is held affords 

 a natural safeguard, for it stimulates the respiratory centre 

 to action with ever-increasing force, and ultimately compels 

 respiration before the o.xygen in the system has sunk to 

 danger-level. However, the risk due to oxygen deficiency 

 can be readily overcome. Hill and Flack have shown 

 (Journ. Physiol, vol. xxxvii.) that if a few breaths of 

 oxygen are taken during quiet breathing, the time for 

 which the breath can be held is generally more than 

 doubled. Not only is the oxygen want of the system 

 thereby eliminated, but, in addition, the oxygen renders the 

 respiratory centre considerably less sensitive to carbon 

 dioxide, and so permits it to accumulate to a greater 

 extent than usual in the body. The same thing holds after 

 forced breathing, and I found that if one to four breaths 

 of oxygen were taken at the end of the forced respira- 

 tion, the breath could be held about twice as long as in 

 absence of oxygen. .After one minute's forced breathing I 

 held my breath for 4m. i8s. ; after three minutes' breath- 

 ing for 6m. 34s., and after six minutes' breathing for no 

 less than 8m. 13s. 



So far as I can ascertain, the world's record for a pro- 

 fessional diver remaining under water in a tank w-as made 

 by Miss E. Wallenda in 1898, when she reached 4m. 455s. 



