49o 
THOMPSON YATES LABORATORIES REPORT 
Of the interesting and important facts which have been ascertained, those 
elucidated by Dr. Carter in his study of outbreaks at Orwood, and Taylor (Miss) 
in 1898, are second to none.' The conditions were such that the intervals between 
the introduction of ' infecting ' cases and the onset of secondary cases could be 
followed with accuracy. Dr. Carter finds that an interval of about fourteen to 
twenty-one days obtains before the first secondary cases occur. The house is then 
in an ' infected ' condition, and exposure for a few hours (for example, in one case 
four hours and a half) can lead to infection, with the incubation interval up to the 
normal four or five days. This was exemplified to us by the history of a case at 
Ouemados, for which we are indebted to Dr. Reed. In a house which had been 
occupied by non-immune officers all last year, two cases of yellow fever occurred this 
summer ; one of these was unfortunately fatal. However, a male and a female nurse 
who had been occupied in tending the patients did not acquire the disease until about 
a fortnight after the death occurred. Other sources of infection could be excluded in 
these cases. No further cases occurred, as the house was cleared and liberally treated 
with perchloride. The slight epidemic, however, spread to other houses down the 
street, although they were detached and surrounded by a small amount of garden 
space. 
This curious and somewhat prolonged interval is suggestive of a development of 
the infecting factor in or about some agent or matter in the domicile. What may be 
the nature of this supposed agent is not yet demonstrated, but the suggestion pro- 
pounded by Dr. C. Fin lay, of Havana, some twenty years ago, that the disease was 
spread by means of mosquitoes hardly appears so fanciful in the light of recent dis- 
coveries in ague convection as appeared in the days when the idea was first broached. 
Dr. Finlay's hypothesis is able to account for several curious points which obtain 
with yellow fever. Thus the limitation of the disease to the 'yellow fever zone,' 
where frost is unknown, the coincidence of yellow fever and rainy seasons, the cessation 
of the disease when the temperature falls below a certain point, and its non-recrudes- 
cence in an infected locality after a frost, are all compatible with an agency, such as a 
gnat, which becomes too sluggish to bite, or indeed which dies out in unfavourable 
climatic conditions. Such a theory also explains the curious spread of the disease 
from house to house, which has already been referred to. Another point is that the 
sanitary condition of a house may be good, and yet it may be severely ' infected.' An 
example of this was shown by the case of one of the leading hotels in Havana, of good 
sanitary repute, but the source of many fever cases this summer. The above sketch 
will suffice to show that some means of transmission by the aid of an intermediate 
host — a town-loving host for this town-loving disease — is to some extent more plausible 
than might be anticipated. Whether that hypothetical host is of the nature of a gnat 
remains unknown. 
1. Neiv Orleans Medical and Surgical Journal, May, 1 goo 
