PROGRESS OF MICROSCOPICAL SCIENCK 99 



jacent papillary layer of tlie corium ; in the former, by the enlarge- 

 ment and increased distinctness of outline of the cells, and by 

 corresponding germinative changes in their nuclei ; in the latter, by 

 the increase of size of the papillae, and by germination of the epithelial 

 elements of the capillary blood-vessels. 



3. It is next seen that the interfascicular channels (lymphatic 

 canaliculi) of the corium are dilated and more distinct ; that the lining 

 cells of these channels are enlarged and more easily recognized than 

 in the natural state ; and that, in the more vascular parts of the 

 corium, the channels are more or less filled with migratory, or lymph, 

 corpuscles. At the same time, the lymphatic vessels, of which the 

 canaliculi are tributaries, can be readily traced, in consequence of their 

 being distended with a material which resembles coagulated plasma. 



4. About the third day after the appearance of the pock, the 

 contents of the dilated lymphatics begin to exhibit characters which 

 are not met with in ordinary exudative processes. These consist in 

 the appearance, in the granular material already mentioned, of 

 organized bodies, which neither belong to the tissue nor are referable 

 to any anatomical type — viz. of spheroidal, or ovoid, bodies having the 

 characters of micrococci and of branched filaments. These last may 

 be either sufficiently sparse to be easily distinguished from each other, 

 or closely interlaced so as to form a felt-like mass. 



6. The process, thus commenced, makes rapid progress. After 

 one or two days, the greater number of the lymphatics of the affected 

 j)art of the corium become filled with the vegetation above described ; 

 and on careful examination of the masses, it is seen that they present 

 the characters of a mycelimn, from which necklace-like terminal 

 filaments spring, each of which breaks off, at its free end, into conidia. 

 In most of the filaments, a jointed structiu-e can be made out, and, in 

 the larger ones, the contents can be distinguished from the enclosing 

 membrane by their yellowish-green coloiu*. 



6. At the same time that these ajipearances present themselves in 

 the coriiun, those changes are beginning in the now much thickened 

 rete Malijighii which are prej)aratory to the formation of the vesicular 

 cavities already mentioned. By a process which the author designates 

 horny transformation, having its seat in the ej^ithelial cells of the 

 middle layer of the rete Malj)ighii, a horny expansion, or stratum, 

 appears, lying in a plane parallel to the surface, by which the rete 

 Malpighii is divided into two parts, of which one is more superficial, 

 the other deeper than the horny layer. Simultaneously with the 

 formation of the horny layer the cells of the rete nearest the surface 

 of the corium imdergo very active germination, in consequence of 

 which the interpapillary processes not only enlarge, but intrude in an 

 irregular manner into the subjacent coriiun. At the same time, the 

 cells immediately below the horny stratum begin to take part in the 

 formation of the vesicular cavities, some of them enlarging into 

 vesicles, while others become flattened and scaly, so as to form the 

 septa by which the vesicular cavities are separated from each other. 



7. The vesicles, once formed, increase in form and number. 

 Originally separate, and containing only clear liquid, they coalesce. 



