658 FILTERABLE VIRUSES— RICKETTSIA 
Von Pirquet tuberculin chisel. The chances of successful vaccination 
by the puncture method are somewhat less than by the linear incision, 
however. The older method of vaccination was through a scarified 
area, varying from a square centimeter to nearly twice that size. The 
crust that forms over such a wound furnishes excellent anaerobic 
conditions for the growth of bacteria, and the thickness of the crust 
offers mechanical opposition to the formation of the vesicles, which 
are prone to appear around the area in consequence. A accination by 
scarification is forbidden by law in Germany. It should be in the 
United States. 
2. TJw Course of the Disease, Vaccinia.— The initial reddened site 
of inoculation soon disappears, leaving only a small scratch or punct- 
ure; about the third or fourth day, however, one or several small 
bright red papules appear, which become vesicular by the end of 
seven days and surrounded with a bright red areola. The contents 
of the vesicle become yellowish, usually from the eighth to the tenth 
day, and discharge a yellowish fluid if they are opened. The contents 
then become desiccated, and a crust forms which drops off in about 
two weeks. 
From the third to the fifth day after the vaccination a febrile reaction 
of 1 or 2 degrees is usually experienced, and the site of the vaccination 
itches intensely and is painful. There is frequently loss of appetite 
and general symptoms of malaise quite out of proportion to the 
amount of local reaction. By the end of the second week the symptoms 
have disappeared and the sunken multilocular scar is the principal 
residual evidence of a successful vaccination. It is generally believed 
that already by the ninth to the eleventh day after inoculation the 
patient is relatively refractory to infection with smallpox virus. 
3. I nnnunity.— The duration of immunity is not definitely known, 
but it is stated to be from seven to ten years on the average. In Ger- 
many, where vaccination has been enforced by law for five decades, 
a child is required to be vaccinated by the end of the first year, again 
about the time it enters school, and a third time at the age of sixteen 
or thereabouts. 
Occasionally a first vaccination is unsuccessful. Frequently old or 
inactive vaccine, poor technique, or a deliberate sterilization of the 
vaccined area with disinfectants are responsible, because man does 
not, as a rule, exihibit immunity to natural vaccinia. Several suc- 
cessive negative results should be obtained before the individual is 
pronounced refractory. 
4. Revaccination.—B.ey accmsition frequently does not lead to a 
"take," but in a fair proportion of individuals a typical reaction may 
take place; this may be an accelerated reaction. The accelerated 
reaction runs a more rapid course than the ordinary reaction and 
reaches maturity usually within four to six days in place of seven to 
ten days. Less commonly an "immediate" reaction is met with; the 
site of inoculation becomes reddened and the lesion is greatest within 
