Vaccine virus is the specific principle in the material obtained from the skin eruption of calves1 having a disease known as vaccinia. The eruption begins as a papule, which develops into a vesicle, and later a pustule. For the purpose of propagating vaccine virus the material is usually taken from the vesicles when fully developed. This may be somewhere between the fifth and the eighth day after the animal has been vaccinated.
The material should be taken only from typical, unbroken vesicles, and is usually obtained by scraping with a curette. This material scraped from the skin eruption is called vaccine "pulp." The fluid which exudes after the pulp is taken is called vaccine "lymph." Both the pulp and the lymph are mixtures containing epithelial cells, serum, blood, leucocytes, products of inflammation, debris, bacteria, etc., in varying proportions.
The use of the pulp for the purpose of vaccination is of comparatively recent
EOSENAU MJ. VACCINE VIRUS. JAMA. 1910;LIV(4):250–251. doi:10.1001/jama.1910.92550300001001a
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