WATA>\\P.E: ON THE SO-CALLED BLACK-HEAD OE TUKKEY. 71 



loaded with the ])ar:isitic cells. 



It is notewortliy that duriair tlie earlier stages of infection, the parasites are 

 conti lied to the tniiica prdpria, and that tliey invade bv stages the submucosa and 

 even the blood vessels. Changes craisod by tlie parasites in the snbrancos.i, are, on 

 the other hand, (piite different from those snffered by the tunica propria just stated : 

 the structural elements, tln^ fibers, are, in contrast to the cas<^ in the tunica j)ropria, 

 entirniouslv added, s:> tiiat the laver is woven with reticulated fibers of thick 

 me.^hes. The meshes of the reticulated tis.>ue arc filled up with the parasitic cells. 

 It is furthermore not unreasonable that there is, within this layer, produced a 

 certain pressure. This pressure and the added tissue-elements jirobably take })art 

 to a great extent in causing the coecal walls to be thickened. 



L: stly the mncous epithelium is not directly attacked by the parasites, but is 

 broken uj) in conscipience of the enormous bulging ^)f the strata underlying it, 

 i. e. the tunica piopria and the subnnicosa. 



The Lieberkidm's ervpts, which nre formed of nmcous epithelium, are ;ilso 

 filled up with the pai-asitic cells ; their walls suffer, of course, a damage to a 

 ceitain extent. 



Xow we arrive at the question, how the parasites leach the place, the tunica 

 propria, where they are found in earlier stages of the disease. I have no positive 

 evidence in proving the actual invading of the ])arasites ; there are, honever, several 

 negative infeiences as to the possibihty in regard to theii- invasion. In the first 

 place, it may be assumed that the parasites arrive at the tunica propria by an 

 indirect wav from the blood-ves.-:els which tliey enter at a far distant [)lace. But this 

 assumption could not have bean proved : so far as my oli-ervations extended, nowhere 

 were the parasites ibund in the blood -ves,-^els at the time when they make their fiist 

 appearance in the tunic.i propria. 



In the i^cond place, the Lieberkühn's crypts may be taken as the entrance of 

 the para.sites ; for the tubes are not only in a situation appropiate for the entrance 

 of the parasites, but they are, in fact, very often filled up with the paras'.tic cells. 

 There is, however, an important factor which should not, at any late, be overLioked 

 for tlic elucidation of the problem : the parasitic cells are detected always in the 

 outside as well as in the inside of the tube's wall, i. c. in the tunica propria and in 

 the tube's interior, and they never occur in the latter part alone. It is. therefore, 

 evident that the para.sites in the tube's interior ]tu-h liieir way from witliour into 

 the interior, and not in the inversed direction : in other words, thev come into the 



