ETIOLOGY OF YELLOW FEVER 683 



for ten minutes. On the other hand, blood or serum was found 

 to be still infective after having been passed through a Berke- 

 feld filter. This was confirmed by the French Commission, 

 with the additional result that the virus passes through a 

 Chamberland F filter, but not through a Chamberland B. 

 These facts would show that the parasite is of extremely minute 

 size, and apparently belongs to the group of ultra-microscopic 

 organisms. In accordance with this, attempts to find by 

 microscopic examination the yellow fever parasite, either in the 

 blood of patients suffering from the disease or in the tissues of 

 infective mosquitoes, have been attended with negative results. 

 In 1912, however, Seidelin described the presence in the blood 

 of a minute intracorpuscular parasite resembling a piroplasma : 

 it was found both in the erythrocytes and in the leucocytes. 

 He regards it as a new genus, to which he has given the 

 name paraplasma jlavigenum, and believes that it is the 

 causal organism. Although he found it in a large proportion 

 of cases of the disease, his results have not yet been con- 

 firmed by others. It has been stated that it, is possible to 

 produce yellow fever in the chimpanzee by the injection of 

 blood from a patient. 



Though nothing has been determined regarding the actual 

 nature of the virus, yet the results already obtained have 

 supplied the basis for preventive measures against the disease, 

 these being directed towards the destruction of mosquitoes and 

 the protection of those suffering from yellow fever, and also the 

 healthy, against the bites of these insects. Already a striking 

 degree of success has been obtained in Havana. Such measures 

 came into force in February 1901, and in ninety days the town 

 was free of yellow fever, and for fifty-four days later no new 

 cases occurred ; and although subsequently the disease was 

 reintroduced into the town, no difficulty was experienced in 

 stamping it out by the same measures. In recent years the 

 results have also been highly gratifying, and the disease may 

 be said to be practically eradicated from Havana. In other 

 large centres of population, for example Rio de Janeiro, equally 

 successful results have been obtained, and epidemics in limited 

 areas would appear to be now under control if the proper 

 measures are taken. In striking contrast to this is the fact that 

 in certain places where preventive measures have not yet been 

 satisfactorily instituted, owing to the population being scattered 

 or other causes, the mortality from yellow fever still remains 

 high. 



