CAUSE A PROTOZOAN 257 



" The Myxococcidium stegomyice is not an animal parasite. Yeast cells some- 

 times simulate the coccidia in form and staining reaction. 



" The infection of yellow fever is in the blood serum early in the disease. 

 N"© abnormal elements that bear a causal relation to the disease can be detected 

 in the serum or in the corpuscles with the best lenses at our command. 



" The infective principle of yellow fever may pass the pores of a Pasteur- 

 Chamberland B filter. 



" Particles of carbon visible with Zeiss lenses pass through both the Berke- 

 feld and Pasteur-Chamberland B filters. 



" Because the virus of an infectious disease passes a Berkef eld or Pasteur- 

 Chamberland B filter it does not necessarily follow that the parasite which 

 passed the filter is * ultramicroscopic/ or that it may not have elsewhere another 

 phase in its life cycle of large size. 



" The filtration of viruses may succeed or fail, depending upon the character 

 of the filter, the diluting fluid, the pressure, time, temperature, motility of the 

 particles, and other factors. 



" The period of incubation of yellow fever caused by the bites of infected mos- 

 quitoes is usually three days, sometimes five days, and in one authentic instance 

 six days and two hours ; but when the disease is transmitted by such artificial 

 means as the inoculation of blood or blood serum the period of incubation shows 

 less regularity. 



" Yellow fever may be conveyed to a nonimmune by the bite of an infected 

 Stegomyia fasciata; but the bites of Stegomyia which have previously (over 

 twelve days) bitten cases of yellow fever do not always convey the disease. 



" Fomites play no part in the transmission of the disease. 



" The tertian and sestivo-autumnal malarial parasites will not pass the pores 

 of a Berkef eld filter." 



The causative organism of yellow fever still remains unknown.* 



Carroll, of the American commission, in almost the last paper before his 

 lamented death, and which forms the chapter entitled " Yellow fever " in 

 volume ii of Osier's Modern Medicine, summarizes, on page 747, the arguments 

 which favor the protozoal character of the organism presumed to cause the 

 disease : 



" Notwithstanding all the efforts that have been put forth in that direction, 

 the specific organism of yellow fever still awaits recognition. The arguments 

 opposed to the idea that the invisible causative agent of yellow fever is a bac- 

 terium are: (1) it has never been recognized nor cultivated; (2) according to 

 the French Commission the blood of a patient loses its power to infect within 

 two days if exposed to the air, and within five days if air be excluded; (3) the 

 absolutely non-contagious and even non-infectious character of the disease under 

 conditions otherwise favorable but in the absence of the mosquito. The argu- 

 ments in favor of its being a member of the animal kingdom are : (1) its obliga- 

 tory parasitic existence in man and the mosquito, alternately; (2) the necessity 

 for the lapse of a definite period, two weeks or more after the ingestion of the 

 blood, before the mosquito becomes capable of infecting; (3) the restriction of 

 the hosts to a single vertebrate and a single genus of invertebrates which points 

 to a definite cycle of development ; (4) the rapidity of development of the para- 

 site within its invertebrate host is governed by conditions of external tempera- 



* Quite recently, claims of the discovery of the causative orsranlsm of yellow fever have heen 

 published by Dr. Harald Seldelin (Zur Aetlologle des gelben Flebers. Berl. kiln. Wochenschr., 

 no. 18, pp. 821-823, 1909 ; Protozoon-like bodies in the blood and organs of yellow-fever patients. 

 Journ. Pathol. & Bacterlnl., vol. 15, pp. 282-288, 1911 ; The etiology of yellow fever. Yell. Fever 

 Bull., vol. 1, no. 7, pp. 229-258, plate. 1911). 



