Immunity. 299 



different forms of pox, experiments prove that horses and cattle 

 may be immunized with variola against vaccinia, man with 

 vaccinia against the variola; but a similar reciprocal action of 

 vaccinia and ovina is very questionable. 



The mode of development of the immunity is not yet sufficiently 

 known. According to Beclere, Chambon & Menard, as well as Martins, 

 the blood of animals which were inoculated with vaccinia or with 

 variola, and in a still greater degree that of persons who have passed 

 through an affection of pox, contains substances which prevent the 

 pox lymph from exerting its action. At the same time they have an 

 immunizing action, and the favorable results obtained in recent times 

 with the blood serum of highly immunized animals, especially sheep, 

 make this conception^ very probable (see p. 317), however the nature 

 of these substances is not even remotely known. As the pox eruptions 

 develop only several days after the penetration of the virus into the 

 blood circulation, potent blood serum may exert its immunizing action 

 even during the time of incubation. The immunization may be success- 

 fully accomplished also with lymph heated to 60° (Siipfle) and with 

 filtrates through porcelain (Green). 



The inoculation of virulent lymph into the skin results 

 in a slowly developing immunity, and in all probability is due 

 1o the influence of the substances absorbed from the point of 

 inoculation, as in such instances the virus itself does not pass 

 into the blood circulation (Siipfle). As a rule only a local 

 eruption develops after such an infection; if however the 

 inoculated part of the skin is removed 24 hours after the 

 inoculation, a generalized pox eruption develops (Chauveau). 

 In the first instance an immunity results already during the 

 development of vesicles, and the virus which later penetrates 

 into the blood circulation can no longer attack the tissues, while 

 in the second case the resistance of the tissue has not been 

 increased to a degree in which it could oppose the pathogenic 

 action of the virus by the removal of the source from which 

 the immunizing substances develop. In infections resulting 

 from inhalation the virus enters directly into the blood circula- 

 tion, and thereby meets everywhere unresisting tissues, and 

 in such cases a more or less generalized pox eruption invariably 

 develops. 



Offspring from animals which recovered from a general 

 or local variola during pregnancy are immune, but this im- 

 munity becomes gradually weaker (in lambs according to 

 Duclert from the 3d-4th month on), and disappears entirely 

 in the second generation. The pox immunity is only excep- 

 tionally inherited, and even in such cases it affords only a partial 

 and passing protection (Siipfle). 



The etiological relation of human and animal pox to each 

 other is not sufficiently established. The uniform anatomical 

 structure, and the similar development of the characteristic 

 vesicles indicate the etiological identity of the different forms 

 of pox. However observations relative to the reciprocal inf ec- 



