208 CONTAGIOUS DISEASES. 



down tlie cuticle to the cutaneous glands, tlius producing the 

 pit or umbilicus. 



Dr. Gustav. Simon differs from the above opinion, and says 

 that " variolous pustules are not always constituted alike. In 

 many cases, where a central depression clearly existed, the epi- 

 dermis was entirely raised from the subjacent cutis ; and only 

 at the spot corresponding with the umbilicus were both mem- 

 branes united by a thin, whitish cord, which, as the microscope 

 evidently showed, was a hair sac. The presence of a hair sac is 

 not, however, essential to the production of an umbilicus, and a 

 remarkable peculiarity, first noticed by Eayer, characterises the 

 variolous vesicle in those parts of the body where neither hair 

 sacs nor sebaceous follicles exist. Eayer found, on removing the 

 epidermic cap of the vesicle, and wiping off the fluid collected 

 beneath, that a little elevation existed in the centre of the 

 denuded corium, whilst the circumference was visibly depressed 

 below the level of tlie neighbouring healthy cutis. These eleva- 

 tions were found by Dr. Simon, who examined them micro- 

 scopically, to consist of a file of papilla? of normal or nearly 

 normal size and condition, while the depressed margin is paved 

 with papilla? bent down or flattened. The explanation is simple. 

 At the centre of the vesicle an organic connection (from some 

 yet unexplained cause) exists between the cutis and cuticle, and 

 at this point no fluid is effused; but around this centre, exudation 

 of fluid occurs without impediment, and tends to force the cutis 

 and cuticle asunder." — {British and Foreign Mcdico-Cliirurgical 

 Review, vol. iii.) 



About the ninth day of the vaccine disease a purely vesicular 

 eruption makes its appearance upon the udder. Within twenty- 

 four hours the vesicles contain a pellucid serous fluid. On 

 the following day the fluid becomes turbid, the cuticle collapses 

 or bursts, and a thin, brittle, flimsy crust forms, and speedily 

 falls off. Successive crops continue to form and dessicate for 

 three or four weeks. 



It is difficult to trace the origin of an outbreak of variola 

 vaccinae in a herd of cattle. Outbreaks of it seem to follow 

 similar inexplicable paths to those which characterise other con- 

 tagious diseases. Cases spring uji now and then which appear to 

 be solitary, and cannot be traced to a cause. At other times it 

 seems to be epizootic, and prevails at several farms at the same 



