June 15, 1905] 



NA TURE 



151 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 tp return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. "[ 



The Possibility of Reducing Mosquitoes. 



In his able review of James and Listen's interesting 

 " Monograph of the Anopheles Mosquitoes of India," pub- 

 lished in your issue of May 25, Dr. Stephens recapitulates 

 the arguments of these authors in favour of their hypo- 

 thesis that " the task of materially reducing the number of 

 Anopheles in any place will undoubtedly be one of great 

 magnitude." As the subject is one of the greatest sanitary 

 importance, it may perhaps be advisable to add that the 

 validity of these arguments is by no means accepted by 

 all students of the subject. They are based for the most 

 part on the results of some anti-mosquito work done at 

 Mian Mir by Dr. Christophers and Captain James. 

 Perhaps those of your readers who are not medical men 

 may not be cognisant of the fact that an exhaustive and, I 

 think, destructive criticism of this work has been pub- 

 lished by Colonels Cronibie and Giles, Captain Sewell, 

 and myself — vide British Medical Journal, September 17, 

 1904, and Journal of Tropical Medicine, 1904. My own 

 conclusions were that the operations cost too little to be 

 effective, and that no exact method was employed for 

 enumerating the numbers of mosquitoes present before and 

 after their commencement. So far as I am aware. Dr. 

 Christophers and Captain James have not replied to our 

 criticisms, and I therefore feel justified in assuming that 

 the case has gone against them by default. I should add 

 that I hear on very good authority that the operations at 

 Mian Mir are now being continued on a better basis. 



The principal argument of our authors appears to be 

 that the local reduction of mosquitoes will be wholly or 

 largely impracticable because of immigration of the insects 

 from outside. Thus they mention four methods by which 

 -Anopheles are dispersed, namely, by flight, by streams, by 

 carriages, and by gradual spreading in all directions " by 

 short stages," and think that the last method is "over- 

 looked by those who have no intimate knowledge of 

 mosquito habits, but who readily draw up schemes for 

 their wholesale destruction." I fear that these very self- 

 evident facts were well known and carefully considered 

 long before the authors commenced their researches, and, 

 moreover, that they do not by any means establish their 

 case. It is quite obvious that a considerable number of 

 mosquitoes must always find their way by diffusion into 

 any area of operations; but this is not enough. What 

 the sceptics have to prove is that the number of immigrants 

 must be so large as nearly, or completelv, to compensate 

 for the local destruction. This is quite a different pro- 

 position, and one which will, I think, tax their ingenuity 

 to maintain. If the local mosquito-density is to remain 

 the same in spite of local destruction, it can only be by 

 means of an abnormally large compensatory immigration 

 setting in coincidentally with the commencement of the 

 work of reduction. But what is there to determine such 

 an extraordinary and suicidal influx? Mosquitoes do not, 

 like a gas, exist under a pressure which compels them to 

 fill up a vacuum, and we can scarcely suppose that they 

 voluntarily move in the direction of their own destruction. 

 But, even if they do rush in to fill the local vacuum, thev 

 must, in order to do so, forsake the outlying tracts of 

 country (which will be correspondingly benefited bv their 

 absence), so that the total average reduction over the 

 whole area influenced by the operations will be exactly 

 the same whether migration takes place or not — an .'irgu- 

 ment which appears to have been overlooked bv the 

 sceptics. 



Owing to the fact that the to and fro movements of all 

 random wandering must tend to annul each other — that 

 is, that the vectorial sum of such movements must tend 

 to zero — I think that migration is not likely seriously to 

 counteract the effect of anti-propagation measures. I 

 should like to refer those Interested In this part of the 

 subject to a paper by me, published in the British Medical 

 Journal for May 13, in which I have endeavoured to 



NO. 1859, VOL. 72] 



approach the subject analytically. My results agree with 

 those of the late Mr. Ronald Hudson, who kindly com- 

 menced a similar analysis for me shortly before his 

 lamented death, and also, I may add, with general ex- 

 perience, which shows that though a few mosquitoes may 

 occasionally wander to considerable distances, the large 

 bulk of them remain near their breeding pools. I venture 

 to think that those who would prove the converse must 

 do so, not by citing Individual cases of long wandering, 

 but by making a much more exact numerical determination 

 of the amount of Immigration than they have yet 

 attempted, and by showing that it greatly exceeds the 

 local birth-rate — a somewhat ditificult task. That their 

 observations are not always those of others may be seen 

 from the following quotation from Dr. Malcolm Watson's 

 report on the highly successful anti-malaria measures 

 carried out In the Federated Malay States {Journal of 

 Tropical Medicine, .April i, p. 104) : — " A definite improve- 

 ment In the health of Klang was evident when only the 

 swamps nearest to the main groups of houses had been 

 dealt with, and while other swamps within the town were 

 still untouched. The mosquitoes from these did not appear 

 to travel any distance, and there has been no evidence of 

 dangerous immigration of Anophellnes from the extensive 

 breeding places which until the middle of 1904 existed just 

 outside the town boundary, and some of which still 

 remain." 



So far as I can see, the case must be the same for 

 mosquitoes as for most other organisms, including man. 

 We should be very much surprised if anyone were to 

 maintain that the population of the British Isles, for 

 instance, would remain the same after abolition of the 

 birth-rate. Why, then, should we assume such a pro- 

 position for mosquitoes? Ronald Ross. 



The Romance of the Nitrogen Atom. 



The letter of Dr. F. J. Allen (Nature, May 4) on the 

 critical temperature of living substances has interested me 

 immensely. The Ideas contained in It have often presented 

 themselves to me in a crude way, and I hope Mr. Allen 

 will find opportunity for elaborating them. I have often 

 thought, when pondering over what one may venture to 

 call the versatility of nitrogen, that a useful book might 

 be written on the chemistry of the nitrogen compounds, 

 including the mineral and organic compounds of that 

 element In one view. If It did no other service it would 

 help to save the mind of the chemical student from being 

 enslaved by the phrase, " the chemistry of the carbon 

 compounds." If the phrase " Ohne Phosphor kein 

 Gedanke " is true, may we not with equal truth say 

 " Ohne Stickstoff kein Leben "? The marvellous powers 

 stored in the carbon atom are sufficiently en evidence in 

 chemical science ; yet may we not recognise the nitrogen 

 atom as the magic " demon " (borrowing a figurative 

 term from Clerk Maxwell) that holds the wand, that (under 

 given conditions such as are noted by Dr. Allen) turns 

 the atoms of oxygen and hydrogen hither and thither In 

 the multiplex atomic relations of growth and metabolism 

 in the living organism, and especially In that little under- 

 stood complex we call chlorophyll ? We know that the 

 inert N. molecule of the atmosphere Is made up of atoms 

 which, in the nascent state, are possessed of great chemical 

 energy, and we may fairly, I think, explain (he Inert- 

 ness of ordinary atmospheric nitrogen by the stability of 

 Its molecule (N,) as arising out of a difference in the ionic 

 constitution of the two atoms which form the molecule. 

 Is it not here that v;e may seek for the explanation of the 

 otherwise puzzling fact that in the extremely stable com- 

 pound NH, the nitrogen atom is trivalent, while In the 

 oxides, halldes. Sec, it is pentavalent? The action of the 

 nitrogen atom, in the way suggested by Dr. Allen, is 

 illustrated by the well known necessity In the fertilisation 

 of soils for the conversion of NH, into nitrates of alkaline 

 bases, in order that the nitrogen in a more <inrfn6/e state 

 of combination may do Its special work in the internal 

 economy of the plant. I recollect discussing this matter 

 some years ago with Dr. Voelcker, when I had the 

 pleasure of meeting him at an agricultural gathering in 

 this neighbourhood. The modern idea of ionlsation of 

 atoms seems also to throw light upon the fact that N^ 



