RABIES, SMALLPOX, VACCINIA AND FILTERABLE VIRUSES 433 



sied after the pulp has been curetted from the inoculated skin of the 

 abdomen to be sure that no disease exists in the calves. The virus is 

 afterward tested for pus organisms, tetanus, and foot and mouth 

 disease. 



Very important is the test for tetanus. Cultures are grown anaerobically for six 

 days, then filtered and the filtrate inoculated into guinea-pigs and these latter 

 watched for ten days to note evidence of tetanus. 



If found free from any harmful germs the vaccine is then tested upon children for 

 potency. Incision is the proper method of vaccination, as by scratching with a 

 needle, two lines i inch long and i inch apart. Scarification should never be 

 practised. 



Guarnieri in 1892 first observed small bodies near the nucleus of infected epi- 

 thelial cells. He called them Cytoryctes vaccinia. Calkins regards these bodies 

 as well as the Negri bodies as being rhizopods and the distributed chromatin as 

 idiochromidia (granules of nuclear chromatin within the cytoplasm). 



THE FILTERABLE VIRUSES 



The first disease of which the virus was found to be capable of pass- 

 ing through the finest porcelain filter was that of foot and mouth 

 disease (Loffler and Frosch, 1898). 



The filter which is ordinarily used for testing for the passage of such 

 disease agents is the Berkefeld filter, one made of diatomaceous earth. 

 The filter should be new and sterilized before use. The material 

 should be diluted with saline before filtering. One may use slight 

 suction from a filter pump. The filtration should occupy only a short 

 time, not exceeding two hours. 



Of the infections belonging to man, in which such a passage of blood 

 or serum through the pores of a porcelain filter, capable of keeping 

 back even such a small bacterial organism as that of Malta fever, but 

 which does not hold back their virus, we have the following: foot and 

 mouth disease, trachoma, molluscum contagiosum, vaccinia, variola, 

 rabies, typhus fever, measles, scarlet fever, yellow fever, dengue, 

 Papataci fever, poliomyelitis and coryza. It has been suggested that 

 the virus of cerebrospinal meningitis may be a filterable one. 



Hog Cholera Virus. Very interesting is the history of the virus of hog cholera or 

 swine fever. This was supposed to be due to an organism of the hog cholera group, 

 B. aertrycke (identical with B. cholera suis and B. suipestifer). This organism 

 belongs to the "enteritidis" group and is more common as a cause of food poisoning 

 in man than the better known Gaertner bacillus. Recently the group of organ- 

 isms, including the paratyphoid B., but not A, as well as the hog cholera group, 

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