CHAPTER XXVI. 

 THE FILTERABLE MICROBES. * 



The Virus of Foot-and-mouth Disease. This filterable or- 

 ganism occurs in the vesicles present in the mouth and on the 

 feet of the diseased animals, and also in the milk of cows suffering 

 from foot-and-mouth disease. The virus was shown to be filter- 

 able by Loffler and Frosch in 1898. It is rendered inert by heat- 

 ing to 50 C. for 10 minutes. Animals are immune after recovery 

 from the disease. Cattle and swine are naturally susceptible 

 and a few cases of the disease have occurred in man. Nothing 

 definite is known concerning morphology or cultures. The in- 

 fection seems to be transmitted with the food as well as by 

 inoculation. 



The Virus of Bovine Pleuro-pneumonia. This organism is 

 present in the- affected lungs and in discharges from the respira- 

 tory tract of cattle suffering from pleuro-pneumonia. Nocard 

 filtered the virus through a Chamberland "F" filter in 1899. It 

 is rendered inert by heating at 58 C., but retains its virulence in 

 glycerine for weeks and resists freezing. Cultures have been 

 obtained by the collodion-sac method by Nocard and Roux. The 

 organisms in such cultures are extremely minute and variable in 

 form. Some of them are spirals and others approximately spher- 

 ical. Immunity follows recovery from the disease, and has been 

 induced artificially by inoculation with cultures and also by inocu- 

 lation with virulent exudate from the lung of a dead animal into 

 the subcutaneous tissue of the tail of the animal to be immunized. 1 



The Virus of Yellow Fever. 2 This organism occurs in the blood 

 of man at least during the first two or three days of an attack of 



1 Kolle and Wassermann, Handbuch, 1912, Bd. I, S. 928. 



2 The publications of Reed, Carroll and their associates have been issued as a 

 volume entitled Yellow Fever, U. S. Senate Document No. 822, 6ist Congress, 

 3rd Session, 1911. 



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