Maech 16, 1906.] 



SCIENCE. 



403 



that apparently healthy negro children in 

 the pestilential districts of Africa constant- 

 ly carry large numbers of malarial para- 

 sites in their blood, explains the source 

 from which the mosquitoes obtain these 

 parasites; it also explains the relative im- 

 munity against this infection enjoyed by 

 the negro. 



If we now consider the numerous points 

 of similarity between malaria and yellow 

 fever they will be found to be very striking. 

 Both are diseases of low-lying districts; 

 both infections are contracted chiefly at 

 night; both may be conveyed by direct 

 inoculation of the blood of a patient; both 

 are most prevalent in the places and sea- 

 sons where and when mosquitoes are most 

 numerous; both infections are impossible 

 after severe frosts, which cause the mos- 

 quitoes to hibernate. These constitute 

 strong points of resemblance between the 

 two diseases, which differ from each other 

 in that the duration of yellow fever is very 

 short, while malarial infection may persist 

 for years. Unfortunately, the parasite of 

 yellow fever has never been found, in spite 

 of claims to the contrary, and notwith- 

 standing the use of the best powers of the 

 microscope, and even the ultramicroscope, 

 in the efforts of skilled observers to dis- 

 cover it. That there is a yellow-fever 

 parasite we feel assured, because it is not 

 possible to explain the continuous propaga- 

 tion of the disease upon any other hypoth- 

 esis, and apart from its invisibility, the 

 manifestations of its presence are in com- 

 plete accord with the behavior of parasites 

 that are well known. "We must not forget 

 that the minimal limits of creation in na- 

 ture may be beyond our conception, and 

 we must be prepared to learn, if necessary, 

 that there are living bodies too minute to 

 be defined with our present instruments. 



The report of the latest scientific investi- 

 gation of this disease by Otto and Neu- 

 mann, of Hamburg,^ members of the 



German commission, working in Rio de 

 Janeiro within the past year, states that 

 they were totally unable to find anything 

 either in the blood or in the cerebro-spinal 

 fluid of patients suffering with yellow fever, 

 that could not be found in similar material 

 obtained from persons suffering with other 

 diseases and from persons in good health. 

 In this work they used the viltramicroscope 

 of Siedentopf and Zsigmondy. Neither 

 could they find anything in the infected 

 mosquito after dissecting it in the fresh 

 state, nor after hardening and sectioning 

 it, that they felt justified in regarding as 

 the cause of the disease. 



How then are we to explain this failure to 

 discover a parasite in an apparently para- 

 sitic disease? And, if a parasite be pres- 

 ent, to what class does it belong? It seems 

 quite rational to exclude it from among the 

 bacteria because: (1) It has never been 

 cultivated nor stained by any of our known 

 methods; (2) the work of Marchoux, Salim- 

 beni and Simond has shown that the blood 

 of a patient after its withdrawal loses its 

 power to infect within two days, if kept 

 exposed to the air, and within five days if 

 air be excluded; (3) the disease has been 

 shown to be absolutely non-contagious in 

 regions where Stegomyia fasciata is not 

 present, i. e., in Petropolis near Rio de 

 Janeiro; (4) we know no bacteria that live 

 in the tissues of animals, as the yellow- 

 fever organism does in the mosquito, for 

 months, as a harmless parasite. The log- 

 ical conclusion, therefore, would seem to be 

 that the parasite of yellow fever belongs to 

 the animal kingdom, because: (1) It is 

 absolutely necessary for its continued exist- 

 ence that it pass alternately through man 

 and the mosquito, and its parasitic existence 

 in these hosts is obligatory; (2) the fact 

 that a period of about two weeks or more 



^M. Otto and R. O. Neumann, Zeitsehrift f. 

 Hygiene u. Infectionskrankheiten, LI., 3, Novem- 

 ber, 1905. 



