56 EXPERIMENTAL RESEARCHES 



discovery, which represents an epoch in our 

 campaign against disease and the beginning 

 of the era of immunisation. I shall therefore 

 enter only into one question, which throws a 

 little light upon that modification of the variola 

 virus which is produced by its passage through 

 the cow. As you know, animals are also affected 

 with small-pox-like diseases which are closely 

 related to human variola. Such diseases are 

 the so-called " sheep- pox " and " bird-pox." 

 The latter affection has recently been studied 

 at my Institute by Dr. Sticker and Staff-Surgeon 

 Marx. It is easily transferable by cutaneous 

 inoculation to fowls and pigeons, and produces 

 extensive small-pox-like hypertrophy of the 

 epithelium. In the diseased epithelial cells 

 highly staining spherical cell-inclusions are 

 found, which must be identified with the cor- 

 puscles of Guarnieri that are found in epithelial 

 cells infected with small-pox or vaccine. Ani- 

 mals which have passed through the disease 

 have thus acquired a complete immunity against 

 subsequent infections. 



As was shown by my assistants, the virus of 

 bird-pox can be filtered through filter-candles. 

 It can be transferred to fowls and pigeons. In 

 fowls the virus retains its pathogenic properties 



