May 23, 1918] 



NATURE 



225 



Mill rids uttered by angry birds, but like those that 

 i li.Liht be made as a feeble protest against some over- 



wering influence; and the whole behaviour of the 



(Is was utterly unlike that of a crowd deliberately 

 iiiobbing a bird of prey witli angry noises. I have 

 witnessed this on several occasions, but have not seen 

 1 similar demonstration against a snake. 



I would ask readers to note, in the professor's 



ond letter, the difference in the behaviour of the 



ds from that which I have described. 



■ ■ Mr. Kershaw speaks of ' a great hubbub ' ; Mr. 

 Ilockin of the birds as ' shrieldng for all they were 

 worth.' This is surely something of a very different 

 urder from the ' faint chirps ' of apparently unwilling 

 birds which I heard. Indeed, they at once reminded 

 me of the nightmare in which one attempts to cry 

 tiut and run away, and can do neither! 



■ I still believe that it was a case of ' fascination,' 

 :;lihaugh I do not for an instant imply that it was by 

 >v)me mysterious power emanating from the snake. 



■' May it not be analogous to the strange fascination 

 which the morbid and terrible have for some human 



mgs: 



There are individuals who have a horror of going 

 near to the top of a precipice, for they feel as if they 

 nuist throw themselves over, yet at the same time they 

 foel constrained to go and look at the chasm whicfr 

 ■ fascinates ' them. G. H. Hale Carpenter. 



c/o Medical G.H.Q., Dar as Salaam, 

 March 12." 



. lENTIFIC TESTS FOR THE SELECTION 

 OF PILOTS FOR THE AIR FORCE. 



MODERN aviation by its complex evolutions 

 in a rarefied atmosphere imposes an enor- 

 mous strain upon the bodily mechanisms. It is 

 important, therefore, that the subjects selected 

 for such work shall be in every vi^ay fitted for it, 

 otherwise early breakdown or worse may result 

 to the would-be pilot, in addition to needless ex- 

 pense to the country. The problem of the selec- 

 tion of fit candidates is therefore best approached 

 from the point of view of practical aeronautics. 



Considering the effects of a flight in detail, 

 with increasing altitude there is in the first place 

 a deepening of the respiration necessary to secure 

 an adequate oxygen supply. Later, the pulse 

 quickens, and, since a quickened rate of heart- 

 beat entails increased oxygen consumption, there 

 is established a vicious circle — namely, an in- 

 creased oxygen consumption with a progressively 

 diminishing supply. Therefore! all the bodily 

 devices that render the respiration and the circu- j 

 lation efficient will be called into play — in par- 1 

 ticular the nervous mechanisms controlling the 

 respiration and circulation. Finally, at great alti- 

 tudes loss of muscular power and nervous symp- 

 toms, subjective and objective, supervene, so that 

 the pilot or observer finds it difficult to perform 

 his work efficiently. 



In addition to the effects of altitude, there is., 

 as regards the nervous system, the psychical 

 strain involved during preliminary training, the 

 anxiety of the first solo flights, and, finally, the 

 stress of combatant service. For these reasons 

 it is evident that the candidates for aviation must 

 be of the fittest. As is to be expected, therefore, 

 past experience has shown that candidates with 

 NO. 2534, VOL. lOl] 



a good physique and previous excellence at sports 

 make the best pilots. 



Considering the examination of candidates in 

 more detail, it is important first of all that the 

 candidate shall be able to withstand the effects 

 of work in a rarefied atmosphere. No matter how 

 sound in body and limb, a candidate for the Air 

 Force is useless if he will not wear well under 

 these conditions. From this point of view it is to 

 be borne in mind that previous knowledge of 

 mountain sickness an*d life at high altitudes is of 

 little service, as there is no evidence of any ac- 

 climatisation to altitude in the flying officer. 



At the Aviation Candidates' Board particular 

 attention is devoted to the respiratory system, 

 where, in addition to good, healthy lungs and an 

 efficient vital capacity, it is deemed necessary for 

 the candidate to be able to hold the breath for a 

 considerable period of time. In regard to the 

 last test, it has been shown by careful correlation 

 with more complex tests that the power to hold 

 the breath is closely related to the capacity of 

 the candidate to bear the strain of high altitudes. 



In addition to an organically sound heart, it 

 is also deemed essential by this .Board that the 

 heart shall respond efficiently to work both in 

 resp>ect of increase of pulse-rate and time of 

 return to the normal. This is tested by getting 

 the candidate to step from the ground on to a 

 chair five times in fifteen seconds. The increase 

 in pulse-rate is noted, and the time of return to 

 the rate before the exercise carefully observed. 

 The standards for this test have been set by the 

 examination of a number of successful pilots. 



As regards the circulatory standard, it is held 

 that the difference between the pressure in the 

 circulatory system when the heart is beating and 

 the pressure when the heart is resting shall not 

 be great (more than 50 mm. Hg), nor the latter 

 pressure (the diastolic pressure) too low (below 

 70 mm. Hg). 



In regard to the nervous system, besides signs 

 of good nervous stability, it is deemed Important 

 that the candidate shall have accurate vision ; and 

 examination is particularly directed to rule out 

 cases of concealed hypermetropia, which involves 

 bad landing. A good colour sense is also neces- 

 sary. 



In Allied countries especial attention has been 

 directed to the examination of the labyrinthine 

 mechanism. Although practised, such tests have 

 not so great a vogue in this country. It is to be 

 remarked that, as carried out by means of the 

 revolving chair, the labyrinthine tests yield in- 

 formation in regard to the horizontal canals, 

 whereas in most aerial "stunts " it is the superior 

 canal which is important to the airman. There- 

 fore, if tests for tliis mechanism be employed in 

 great detail, they should also be directed to the 

 investigation of the superior canal. 



A further criticism of these tests is that they are 

 based largely on theoretical considerations, and 

 before standards are adopted in regard to such it 

 i.J; important that a series of healthy and successful 

 pilots should he- examined. Since aviators may 

 emerge from a cloud "on their backs" (that is. 



