EFFECT OF VACCINATION 417 



felt in the vaccine commonly used in vaccination, hence the new 

 form as above designated. This retains the toxic qualities required 

 for immunity, but is so produced that it possesses in addition three 

 very important advantages : namely, it is entirely free from extran- 

 eous organisms, it is available for a large number of vaccinations, and 

 it retains full activity for eight months. It is prepared as follows : 

 — A calf, aged three to six months, is kept in quarantine for a week. 

 If then found upon examination to be quite healthy, it is removed 

 to the vaccinating station, and the lower part of its abdomen anti- 

 septically cleaned. The animal is now vaccinated upon this sterilised 

 area with glycerinated calf lymph. After five days the part is again 

 thoroughly washed, and the contents of the vesicles, which have of 

 course appeared in the interval, are removed with a sterilised sharp 

 spoon, and transferred to a sterilised bottle. This is now removed to 

 the laboratory, and the exact weight of the material ascertained. A 

 calf thus vaccinated will yield from 18 to 24 grams of vaccine 

 material. This is now thoroughly triturated and mixed with six 

 times its weight of a sterilised solution of 50 per cent, chemically 

 pure glycerine in distilled water. The resulting emulsion is asepti- 

 cally stored in sealed tubes in a cool place. At intervals during four 

 weeks it is carefully examined bacteriologically until by agar plates 

 it is demonstrably free from extraneous organisms, when it is ready 

 for distribution. 



The Effect of Vaccination. — The Royal Commission on Vaccination, 1896, 

 concluded (p. 90) that the protection vaccination affords against smaU-pox may be 

 stated as follows : — 



" (1) That it diminishes the liability to be attacked by the disease. (2) That it 

 modifies the character of the disease and renders it less fatal and of a less severe 

 type. (3) That the protection it affords against attacks of the disease is greatest 

 during the years immediately succeeding the operation of vaccination. It is 

 impossible to fix with precision the length of this period of highest protection. 

 Though not in all cases the same, if a period is to be fixed, it might, we think, fairly 

 be said to cover in general a period of nine or ten years. (4) That after the lapse of 

 the period of highest protective potency, the efficacy of vaccination to protect against 

 attack rapidly diminishes, but that it is still considerable in the next quinquennium, 

 and possibly never altogether ceases. (5) That its power to modify the character of 

 the disease is also greatest in the period in which its power to protect from attack is 

 greatest, but that its power thus to modify the disease does not diminish as rapidly 

 as its protective influence against attacks, and its efficacy during the later periods of 

 life to modify the disease it still very considerable. (6) That revaccination restores 

 the protection which lapse of time has diminished, but the evidence shows that this 

 protection again diminishes, and that to ensure the highest degree of protection which 

 vaccination can give the operation should be at intervals repeated. (7) That the 

 beneficial effects of vaccination are most experienced by those in whose case it has 

 been most thorough. We think it may be fairly concluded that where the vaccine 

 matter is inserted in three or four places it is more effectual than when introduced into 

 one or tioo places only, and that if the vaccination marks are of an area of half a 

 square inch they indicate a better state of protection than if their area be at aU con- 

 siderably below this. " 



These findings are well illustrated in the returns of the London Epidemic of 

 SmaU-pox which occurred in 1901-2. These returns are the most recent evidence as 

 to the protection afforded by vaccination. They are as follows : — 



2 D 



