420 AGBICULTUEAL AND INDUSTEIAL BACTEEIOLOGY 



the mieroorganisms concerned. The lesions produced by 

 the two diseases are very similar and it has been found pos- 

 sible in monkeys to immunize against smallpox by inoculat- 

 ing with cowpox and against cowpox by immunizing \mth 

 smallpox. 



Smallpox vaccine is usually prepared from heifer calves 

 from 2 to 4 months old. They are inspected carefully to 

 see that they are not diseased. The animal to be used for 

 the preparation of vaccine is carefully washed and cleaned. 

 The posterior portion of the abdomen and the inside of the 

 thighs are carefully shaved and washed. Shallow cuts are 

 then made both longitudinally and crosswise over a large 

 area. Vaccine from a suitable source is then rubbed intu 

 each one of these incisions. The area is then covered with 

 cotton to protect from dirt. The vaccine is usually ready 

 for collection in five or six days. The inoculated area is 

 then cleaned and the hardened crust removed. The soft 

 material remaining is scraped off and placed in a suitable 

 container. It -is then mixed with glycerin (50 per cent), 

 and triturated in a mortar until it is homogeneous. One- 

 half per cent of phenol is also added. The vaccine is ready 

 after standing for some weeks. Any bacteria which have 

 gained access during preparation have usually been de- 

 stroyed and the virus is ready to be used as a vaccine after 

 having been tested for potency. It may be then used for 

 vaccination in man. At a result of the widespread use of 

 vaccination, the disease has lost most of its terrors for civil- 

 ized people. Usually the immunity resulting from vaccina- 

 tion lasts for some years. 



Stained sections from the lesions characteristic of small- 

 pox show peculiar cell-like inclusions. These are termed the 

 vaccine bodies. Some have contended that these vaccine 

 bodies are artefacts, others that they are living organisms, 

 probably protozoan in nature. Some investigators have 

 even worked out the probable life cycle of the organism. 



