128 MICROBES AND TOXINS 



is chiefly found infecting the large endothelial cells, the 

 " Kuppfer cells," of the capillaries of the liver. 



If the virus of small-pox or of sheep-pox is injected intra- 

 venously, it is simply carried by the blood and settles and 

 multiplies in the skin. In those diseases which Borrel has 

 grouped together under the name of Epithelioses, there exists 

 a fairly strict cellular specificity : the virus only develops 

 vigorously in the interior of epidermal cells, and these cells 

 from the moment of infection take on a special character; 

 they are therefore justly called the receptive cells. The reason 

 why we have failed to inoculate certain diseases is that the 

 proper site of inoculation has not yet been discovered, i.e., the 

 receptive cell, or that this receptive cell requires to undergo, 

 before becoming truly receptive, certain modifications which 

 are still unknown and which we cannot reproduce. 



" In cancer our methods of inoculation in a normal indi- 

 vidual fail to strike the receptive cells and to transform the 

 normal into cancer cells : it is this which constitutes the whole 

 etiological problem of cancer " (Borrel). 



Between the date of penetration of the virus and that of the 

 appearance of the disease there is a period of incubation, during 

 which the virus propagates itself, multiplies and affects the 

 cells on which depend the symptoms. The duration of the 

 incubation varies primarily with the virus, secondarily with its 

 quantity and the path by which it has gained access. For 

 example, the incubation is quite short when experimental 

 septicaemia is produced with a virulent streptococcus, whereas 

 in human leprosy it may last for years. In rabies the period 

 of incubation is shorter, and the disease more violent when 

 the bite is on the face than when it is on the leg. In tetanus 

 (a toxin disease), the longer the incubation the less serious 

 the disease. 



The spirillum of recurrent fever causes a disease of the 

 septicaemic type, i.e., the microbe inhabits the blood. The 

 tubercles characteristic of tuberculosis and glanders represent a 

 reaction of the cells of the mesoderm, while the pustular 

 diseases like small-pox are typically reactions of ectodermic 



