PROPHYLACTIC VACCINATION 281 



to make an oblique puncture of the epidermis. This is repeated so as 

 to produce about six radially disposed punctures, the whole area ex- 

 tending not more than about 5 mm. 



The Intracutaneous Method. The virus is diluted to ten times its 

 volume with distilled water and injected intracutaneously by means 

 of a sterile tuberculin syringe and a fine needle. Two injections about 

 2 cm. apart are made. 



All the methods indicated have given equally good results, but 

 convenience usually dictates the use of the linear incision or the drill 

 method. It is not uncommon in the use of any of these methods to 

 make two or three inoculations. 



Vaccinia. Following the inoculation of the virus the areas usually 

 remain quiescent for from two to four days when slight reddening and 

 itching may develop. Following this a small papule appears, rapidly 

 succeeded by the vesicle. It is important to note that the vesicle is 

 umbilicated and that its multilocular character is indicated by the 

 minute vesicular arrangement of the margin. The vesicle appears in 

 from five to six days, rapidly becomes pustular and is followed by the 

 formation of the crust. The crust is allowed to drop off and subse- 

 quent observations of the scar should show a smooth center, a somewhat 

 scalloped edge and more or less discrete minute marginal scars. During 

 the height of the local reaction the patient may complain of malaise, 

 headache, fever, constipation and other general symptoms. The reac- 

 tion of vaccinoid has been discussed in the chapter on Hypersuscep- 

 tibility (page 243). 



Immunity as the Result of Vaccination. The extent of immunity 

 has been indicated by the decrease in prevalence of smallpox since the 

 introduction of vaccination. It may also be measured by the success 

 of subsequent vaccinations. Kitasato has revaccinated a series of 931 

 cases with successful results as follows : 



After i year 14 per cent. After 6 years 64 per cent. 



After 2 years 33 per cent. After 7 years 73 per cent. 



After 3 years 47 per cent. After 8 years 80 per cent. 



After 4 years 57 per cent. After 9 years 85 per cent. 



After 5 years 51 per cent. After 10 years 89 per cent. 



It will thus be seen that more than 50 per cent, of individuals are 

 susceptible to revaccination four years after the original vaccination. 

 Millard states that the Government reports of the German Confederacy 

 show 91 per cent, to 93 per cent, successful revaccinations in ten years 

 or more after the primary vaccination and concludes that " immunity 

 acquired through vaccination begins to disappear at about the second 

 year and by the tenth year it disappears almost completely." Other 

 investigators have obtained similar results. King reported that in 

 ninety-six adults who had suffered from smallpox at various ages and 

 showed numerous scars of the disease, vaccination was successful in 

 75 per cent. These figures indicate that the older conceptions of the 



