660 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



ing maize (Indian corn) ; according to the other, pellagra is a specific in- 

 fectious disease not necessarily associated with the ingestion of corn. 

 None of the theories concerning causation is supported by reliable positive 

 evidence, but the evidence against the maize theory marshalled by Sam- 

 bon* and others has weakened the almost general belief in that theory which 

 had formerly obtained. A renewed interest in the investigation of pella- 

 gra has developed in Europe, and the recognition of the disease in the 

 United States lias stimulated investigation here also. It is not improbable 

 that these investigations will add something to our knowledge of pellagra, 

 and they may even bring to light some positive evidence in regard to its 

 causation. 



RABIES.f 



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 civilized 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 dogs, and the bite of 

 a mad dog is the most frequent cause of the disease in other animals and 

 in man. It is not uncommon in horses and cattle, and all mammals 

 appear to be suspectible 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 protection 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 excitation, 



* Sambon, British Med. Jour., Nov. n, 1905; Journal of Tropical Med. and Hyg., Sept. 15 

 Oct. i, Oct. 15, and Nov. i, 1910. 

 f Prepared by W. J. MacNeal. 



