8 14 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



According to the second theory, pellagra is a specific infectious dis- 

 ease, in which poor nutrition is one of the important predisposing factors. 

 The epideniiological study* of pellagra, as it has developed and spread 

 in certain parts of the southern United States, has brought to light evi- 

 dence of its infectious nature which, to the writer, seems very convinc- 

 ing. The same investigation has also strongly suggested that the 

 infection is intestinal and trans;mitted in much the same way as is 

 typhoid fever. A specific microbic cause of pellagra has not been 

 identified. . 



Rabies t 



Lyssa or Rabies, the madness of dogs, was recognized as a definite 

 disease of animals and man by the peoples of ancient times. The 

 disease is generally distributed throughout the civiUzed world except- 

 in those places where special measures to stamp it out have been 

 enforced. It does not arise spontaneously but is an infectious disease 

 transmitted from animal to animal. Rabies is primarily a disease of 

 wolves and dogs, and lie bite of a mad dog is the most frequent cause 

 of the disease in other animals- and in man. It is not uncommon in 

 hbfses and cattle, and all mammals appear to be susceptible to it. 



In animals inoculated by injection of the most virulent virus (fixed 

 virus) directly into the brain, the symptoms of rabies appear in four 

 to six days and death usually occurs on the seventh day. Accidental 

 inoculation by the bite of a rabid animal (street virus) rarely causes the 

 symptoms to appear before three weeks, and the onset may be delayed 

 for six months or a year. Not all persons or animals bitten by rabid 

 animals take the disease; probably not more than one in four' or five. 

 This variability depends upon several factors, the most important 

 ones being the virulence and the amount of disease virus, and the part 

 of the body into which it is introduced. Bites upon the face or hands, 

 because of the rich nerve supply of these regions and the lack of protec- 

 tion by clothing, are likely to result in rabies sooner than bites 

 elsewhere. 



After the disease has developed, death is inevitable. In all animals 

 the symptoms are those of a nervous disorder. At first there is excita- 



* Siler, Garrison and MaoNeal. Arch. Int. Med., 1914, Vol. XIV, pp. 292-373; ibid., 1914, 

 Vol. XIV, pp. 453-474; Jaum. A.M.A., I914, Vol. LXIII, pp. 1090-1093, 

 t Prepared by W. J. MacNeal. 



