298 Pox. 



on the method of infection, as well as to some extent upon 

 the condition of the epithelial layer. The skin inoculation, even 

 if effected with strong virus, produces as a rule only a local 

 eruption, as in such cases the virus propagates only at the 

 point of inoculation. A portion of the virus may later be ab- 

 sorbed into the circulation, and be disseminated by the blood 

 to other parts of the skin and mucous membranes, but in these 

 places it is no longer capable of exerting a specific action, as 

 the body has already been immunized during the development 

 of the local eruption (Chauveau). If however inhaled virus 

 enters the lungs, or if it is injected directly into the blood 

 circulation, it is conveyed by the blood stream, to the papillae 

 of the skin, as well as to the tissue of the mucous membranes, 

 where it produces a generalized eruption of pox. The infection 

 is favored by injury of the epithelium, or other pathological 

 conditions (Calmette & Guerin), but the exanthema may de- 

 velop in the absence of any lesions. 



Of course deviations from the rule may occur. If in skin 

 inoculations very virulent or large anjount of virus enters the 

 tissue, or if the local exanthema produced by the inoculation 

 develops slowly, a generalized affection may result, even after 

 cutaneous or subcutaneous inoculation. On the other hand if 

 only a very small quantity, or very weak virus enters directly 

 into the blood circulation, the pox eruptions develop only in a 

 few places or not at all. 



As the virus of variola does not propagate in the blood, 

 the blood of affected animals is not, or only exceptionally, in- 

 fectious. It is infectious only when the 'virus circulates in 

 the blood immediately before the development of generalized 

 pox eruptions. In this manner the fact may be also explained 

 that the excrements and secretions are non-infectious ; the milk, 

 however, is sometimes an exception, namely, in those instances 

 when pox develops in the milk ducts, the contents of which 

 then become mixed with the milk. 



Immunity. Eecovery from pox produces in man and in 

 animals, an immunity which lasts for several years, whether 

 the infection was produced naturally or artificially. The im- 

 munity develops in a generalized pox eruption in the same 

 manner as after a local eruption from inoculation (according 

 to Chauveau a re-infection can not be produced after the fifth 

 day of the development of the pox) , and further a pox exanthema 

 is not absolutely necessary for the production of immunity, 

 as calves may be immunized by intravenous injections of vaccine 

 (Strausz, Chambon & Menard), rabbits by an inoculation into 

 the lungs or into the trachea (Calmette & Guerin), and sheep 

 by intravenous injections of ovine virus (Semner & Raupach), 

 although in such cases the injection does not produce manifesta- 

 tions of variola. 



Eegarding the possibility of reciprocal immunization in the 



