402 



SCIENCE. 



[N. S. Vot. XXIII. No. 585. 



physicians in all matters pertaining to the 

 preservation of health and the prevention 

 of disease. We can not expect that the 

 active practising physician shall keep 

 abreast of all modern advances in scientific 

 medicine, and the numerous contradictory 

 statements that have been made in regard 

 to yellow fever have afforded full justifica- 

 tion for skepticism on the part of such as 

 aim to be conservative. While strong con- 

 servatism is to be commended, persistent 

 skepticism is to be condemned. It is per- 

 fectly justifiable to refuse to receive state- 

 ments that revolutionize our accepted ideas, 

 so long as they are based upon the asser- 

 tions of a single observer or a single set of 

 observers, but vi^hen these observations have 

 been confirmed by competent unbiased per- 

 sons in different parts of the world, such 

 statements must then be accepted as facts, 

 just as we accept other statements in re- 

 gard to history, geography and the sciences 

 in general. 



It is well known that a number of dis- 

 ease-producing animal parasites are never 

 found in nature outside the body of a living 

 host. They pass their whole existence first 

 in one animal and then in another, alter- 

 nately, being carried to and fro by means 

 of biting insects, by the ingestion of in- 

 fested food, etc. It is only necessary to 

 consider here the group of parasites that 

 is transmitted by the blood-sucking in- 

 sects, such as the tick and the mosquito, 

 the latter in particular. We know that 

 the Texas fever of cattle is caused by an 

 exceedingly minute microscopic parasite 

 which spends its whole existence in bovines 

 and in the tick. If cattle are kept free 

 from ticks they can not contract the fever. 

 Furthermore, the tick is now accused, and 

 with good reason, of being the transmitter 

 of relapsing fever. It is equally well 

 known and proved beyond question that 

 the mosquito transmits filarial infection 

 and malarial fever to man. No one would 



think of asserting in print to-day that 

 malaria is contracted through exposure to 

 night air, to unhygienic surroundings or 

 by drinking the filthiest water, for such 

 statements would justly be characterized 

 as absurd. The renowned experiments of 

 Sambon and Low in Italy, in 1900, showed 

 conclusively that persons can live in the 

 most pestiferous malarial regions and re- 

 tain perfect health, so long as they protect 

 themselves against the bites of mosquitoes. 

 In the same year these observers shipped 

 living malaria-infected mosquitoes from 

 Italy to England, where they were applied 

 to two persons in perfect health in a region 

 where malarial fever is unknown. Within 

 a short time both of them suffered typical 

 attacks of malaria, during which the para- 

 sites were frequently demonstrated in their 

 blood. Fortunately the various stages in 

 the development of the malarial parasite in 

 man and in the mosquito can be demon- 

 strated with the microscope. We know 

 that the phases it passes through in the 

 insect are entirely different from its cycle 

 of development in man, and no one has as 

 yet succeeded in demonstrating the exist- 

 ence of this parasite elsewhere than in a 

 living host. Such a demonstration is not 

 necessary, for with our present knowledge 

 we can explain all the known facts relating 

 to the contraction and dissemination of the 

 disease and we can insure absolute protec- 

 tion against it. We no longer attribute 

 malarial infection to the inhalation of gase- 

 ous poisons emanating from swamps in the 

 nighttime, or to bad water. We know 

 that swampy places simply furnish breed- 

 ing grounds for the malaria-carrying mos- 

 quito, which flies at night, and whose bite 

 is necessary for the contraction of the 

 fever. The insect must previously have 

 bitten a person suffering with malaria, and 

 an interval of at least a week must have 

 elapsed, otherwise no infection can result. 

 The recent brilliant discovery by Koch, 



