NATUKE OF VACCINATION 609 



which considerable attention has been paid. They are from 

 1 to 8 p. in diameter, are round, oval, or sickle-shaped, and stain 

 by ordinary nuclear dyes. They lie in the cells in spaces 

 often near the nucleus, and are readily demonstrable in vaccine 

 pustules and also in the experimental lesions -which can be 

 produced in the rabbit's cornea, the larger bodies being defined 

 in the cells towards the centre of the lesion. These bodies 

 have been looked on by many as protozoa, and Guarnieri himself 

 stated that multiplication could be seen occurring in them in 

 fresh lymph; but Ewing and also Prowazek brought forward 

 strong evidence for the appearances being due to nuclear changes, 

 though the latter observer considers them to be the effect of a 

 specific reaction of epithelial cells against the variolous virus. 

 Here, it may be said, Wasielewski has shown that they persist 

 through 46 transfers on the cornea of the rabbit, and, further, no 

 similar appearances- have been found in other skin lesions. 

 Prowazek examined material fixed in a hot mixture of two- 

 thirds saturated perchloride of mercury and one-third 98 per 

 cent, alcohol, washed in 40 per cent, iodine alcohol and stained 

 in Grenadier's hsematoxylin, and found bodies in the epithelial 

 cells 1 to 4 /u, in size, sharply contoured and having ragged 

 edges as if made up of massed chromosomes. These were often 

 broader at one end than at the other, and appearances have 

 been seen which suggest longitudinal division. Prowazek also 

 saw these " lymph-bodies," as he called them, in the lymph, 

 and he inclined to the idea' that they may be protozoa. 

 Bonhoff and also Carini have described spirochetes as occurring 

 in variolous lesions, but this has not been confirmed. Volpino 

 states that in the epithelial cells in corneal infection in rabbits, 

 minute motile bodies can be discerned which do not occur in 

 other corneal inflammations. Future investigations must show 

 what significance is to be attached to these various observations, 

 but the existence of microscopic infective bodies in cells is, 

 according to our view, not incompatible with their having also 

 an ultramicroscopic stage (see p. 622). 



The Nature of Vaccination. — The principle underlying the 

 efficacy of vaccination as a prophylactic is no doubt the establish- 

 ment of an active immunity against the causal organism, which 

 is sufficiently lasting to protect the vaccinated individual for a 

 considerable time. Although the virus of smallpox is unknown, 

 several attempts have been made by indirect methods to 

 establish the existence of reactions similar to those occurring 

 in other immunisations. Thus, in cases of human smallpox 

 and in animals intravenously injected with the vaccine lymph, it 



39 



