350 MOSQUITOES OF NORTH AMERICA 
of a Colon infection, the tertian type being comparatively rare, both in Tampico 
and Vera Cruz. Another point that makes Colon infection seem positive is the 
period of incubation that invariably takes place after primary malarial infection. 
This period has been variously stated to be from one day to several weeks. Our 
own observations (Parker—report to Surgeon-General, October, 1901) on this 
point are limited to a single observation that included three crews, one of a 
steamship and two of schooners at Jacksonville, Fla., during the fall of 1901. 
In this instance the three vessels arrived at Jacksonville from northern ports at 
about the same time, and lay at a badly infected part of the town. Cases of 
malaria appeared simultaneously on all three boats fourteen days after arrival. 
“Dr. D. D. le Favre (Roussky Vratch, October 19, 1902), in an experiment 
on himself, showed that the actual period of incubation of malaria in one in- 
stance was twelve days. 
“Those long periods of incubation in the malignant tertian and quotidian 
aaa account for many infections that have been classed as being yellow 
ever, 
“Tt is a well-known fact, which one of us (Parker) has experienced, that 
steamers lying in Habana Harbor become badly infested with mosquitoes, which 
insects remain on board the steamship during the voyage to Progreso and thence 
to Vera Cruz, appearing at night in the cabins in considerable numbers. 
“It will be seen, then, that there is considerable evidence to support the 
assertion that these insects are constantly being transferred from one locality 
to another through the medium of ocean commerce. In this distribution the 
iron ship, on account of its concealed water tanks, acts in the nature of a 
mechanical host, while wooden vessels, on account of the loosely covered deck 
containers, not only act as a mechanical host, but under favorable conditions, as 
in calm or gentle weather, or lying at anchor, furnish the proper medium for 
the propagation especially of domestic species. 
“ Passed Assistant Surgeon Grubbs, U. 8. Public Health and Marine-Hospital 
Service, has collected data at the Gulf Quarantine Station relative to the trans- 
ference of mosquitoes by vessels. In a total of 82 vessels inspected to determine 
the presence of these insects, he found Stegomyia fasciata in the adult stage on 
three wooden vessels, all from Vera Cruz. One of the vessels was the John H. 
Crandon mentioned above.” 
Surgeon Grubbs’s paper above referred to (Bulletin No. 11, Yellow Fever 
Institute) is interesting as giving the results of an effort to get exact information 
on this point. It is quoted as follows: 
“ At the present time, when evidence is pointing with more and more clear- 
ness to the mosquito as the sole means of transmitting yellow fever, nothing is 
of greater interest to the quarantine officer than to decide to what extent and 
under what circumstances these infecting insects may be carried by vessels. 
“This subject may be approached in three different ways: First, by observa- 
tions on the length of time after leaving infected ports vessels may develop 
yellow fever ; second, by experiments with mosquitoes under artificial conditions 
made to simulate as much as possible those of nature; and third, by actual ob- 
servation of vessels arriving from ports at the time infected or where the presence 
of the Stegomyia fasciata render them liable to infection. 
“ While it will require data obtained by all these means and extending over a 
long period to arrive at any conclusions sufficiently accurate to allow them to 
influence quarantine procedure, still I believe the last method of observation 
cited will throw more light on the subject than the first two. 
“Tt is for this reason that every vessel arriving at Gulf Quarantine Station 
from Stegomyia-infected ports has, since the Ist of July last, been carefully ex- 
