53 
slide. Very beautiful preparations, with the corpuscles lying singly, 
are thus obtained. 
This little apparatus can readily be made at the blowpipe. 
• 
: 
j 
Fig. 1.—Rosenau’s spreader for making blood smears. 
THE PERIOD OF INCUBATION OF YELLOW FEVER. 
The exact period of the incubation of yellow fever is a matter of 
great importance in quarantine and public-health work. For years 
the quarantine regulations of the Marine-Hospital Service required 
a detention of five days, which was considered amply safe to cover 
the period of incubation of the disease. The regulations of the Pub¬ 
lic Health and Marine-Hospital Service, promulgated v August 10, 
1903, lengthened the time of observation in special cases to six days, 
basing this action upon the recent experimental work which has made 
it possible to determine the period of incubation of yellow fever with 
great exactness. 
