December 1, 1916] 



SCIENCE 



789 



Major Ashburn's observations were, that in 

 a given place, men and mosquitoes being asso- 

 ciated, on the removal of the human element 

 the malarial mosquitoes no longer bred in that 

 locality as before, the larvae from being numer- 

 ous became rare, almost, if not quite absent. 

 An instance of this occurred at Miraflores, 

 formerly a hot-bed of malaria, and where 

 Anopheles albimanus bred in abundance. 

 When, in connection with the Canal work, the 

 inhabitants were removed, it was presently 

 discovered that although the breeding condi- 

 tions were quite as good, A. albimanus was no 

 longer breeding in that locality as before, the 

 larvae having become very rare. Contrariwise, 

 that when camps were established in new local- 

 ities where malarial mosquitoes and their 

 larvae were rare or unknown, both adults and 

 larva? presently appeared in greatly increased 

 numbers, and this was followed by a malarial 

 outbreak among the men. Major Ashburn has 

 records of some ninety instances where these 

 conditions, in connection with the establish- 

 ment and abandonment of construction camps, 

 occurred, and it was on this large number of 

 eases that he based his conclusions. 



The question of an " animal barrier " is not 

 a question of whether any given mosquito 

 will attack a horse or a cow or a dog, but 

 whether such animals will prove a protective 

 barrier, against the malarial mosquitoes, for 

 human beings living beyond. Whether dis- 

 ease-bearing mosquitoes will breed except near 

 human habitations is another question, and 

 apparently has several factors, so that it is 

 quite possible that it can not be answered by a 

 general statement. However it is quite cer- 

 tain that these mosquitoes would not have be- 

 come " disease-bearing " if they had not bred 

 near habitations and been in close touch with 

 man. 



The experience of many sanitarians has 

 been that, under usual conditions, to keep the 

 breeding places of malarial carriers at a dis- 

 tance of " four hundred yards " is sufficient 

 to protect the inhabitants of a locality from 

 malaria, and Watson shows that the outer 

 coolie lines are at least the only ones attacked 

 under these conditions. This can only mean 



that the malarial mosquitoes do actually breed 

 near, and not, as Mr. Jennings suggests, " at 

 a distance from human habitations." Also of 

 course this implies the intimate association of 

 malarial mosquitoes and man, and there is 

 nothing in my paper to indicate a lack of 

 recognition of that general condition. It 

 called attention to an entirely new viewpoint, 

 and one that gives a valid reason not only for 

 the usually accepted limit of flight, but to Dr. 

 Watson's observations concerning the outer 

 coolie lines, and even for the long flight re- 

 corded at Ancon, while it suggests a hitherto 

 little recognized need of the protection of 

 human beings in the formation of new camps 

 in heretofore uninhabited sections where ho 

 malaria has been known, or where the larvae 

 of malarial mosquitoes are extremely rare or 

 unknown. 



It is hardly permissible to assume ignor- 

 ance, on the part of a Medical Officer and a 

 worker in preventive medicine, of the litera- 

 ture and labors of many investigators whose 

 work was based on the, at least implied, 

 " association " of mosquitoes and man. Even 

 the average layman knows the story of Man- 

 son's suggestion to Ross. Especially is such 

 an assumption out of place in regard to Major 

 Ashburn, whose work on the transmission of 

 disease by insects, carried on in the Philip- 

 pines as a member of the " Board for the 

 Study of Tropical Diseases " is widely known 

 and accepted as one of the authorities on the 

 subject. 



It is always better to keep " an open mind " 

 on every subject, scientific or otherwise, and 

 certainly to avoid unfair comments on other 

 workers. There is work enough for all, and 

 the various phases of the study of disease are 

 so complicated as to give every part of the 

 subject many sides, and many points of con- 

 tact with the labors of special investigators in 

 other branches. That the whole may develop 

 in a well-balanced and scientifically correct 

 fashion requires harmonious interrelation be- 

 tween these various workers, and a just recog- 

 nition of the viewpoints of others. Mr. Jen- 

 nings's connection with the work in the inves- 

 tigations in the Canal Zone should have broad- 



