194 DENGUE [CH. 



and transmission of dengue in the Philippines, and were able 

 to produce the disease in normal persons by the intravenous 

 injection of 20 c.cs. of blood from an infected patient. The 

 incubation period was two to three days, and was followed by 

 typical attacks of dengue. These authors also found that 

 the pathogenic agent was so small that it would pass through 

 the pores of a filter which retained organisms 0'4 ^ in diameter, 

 filtered serum being equally as infective as non-filtered blood. 



The blood shews little alteration except in the leucocyte 

 count, a slight or well-marked leucopenia being a fairly constant 

 character. The number of polymorphonuclear leucocytes may 

 be reduced to forty or fifty per cent., but at the same time 

 there is an increase of the large mononuclears and lymphocytes, 

 the latter predominating. Some authors maintain that the 

 leucocyte formula remains essentially the same throughout 

 the disease, whilst others are of the opinion that considerable 

 variations occur. Dengue is not accompanied by any anaemia, 

 the red cells remaining normal both in number and ap- 

 pearance. 



Mode of infection. The transmissio7i of this disease is still 

 somewhat obscure in spite of the work of Graham, and Ashburn 

 and Craig. For a long time it was considered to be a highly 

 contagious infection and Diiring recorded a case in which 

 five families that received their washing from the same laund- 

 ress all became infected about the same time and before the 

 other inhabitants. 



Arnold, in 1846, was the first to support the idea that 

 the disease is not contagious and based his theory on two 

 facts noticed in Havana, namely, that the epidemic was 

 localized in the town and did not spread into the surrounding 

 country, and that among the first cases, not any of the patients 

 had been in contact with one another, either directly or in- 

 directly. 



The belief in the contagious nature of dengue has now been 

 abandoned by the majority of investigators, but, in addition 

 to the idea that it is carried by Culex, various other theories 

 of animal transmission have been advanced. In America it is 

 a common idea that the spread of the disease depends in some 



