CROUPOUS EXUDATIONS. 139 



attention almost exclusively to the solid parts of the exudations, 

 which are always more or less altered. 



Rokitansky, who would naturally judge of the nature of the depo- 

 sitions solely from their physical character, has arranged croupous 

 exudations in three subdivisions, a mode of division which has 

 been much objected to, but which is undoubtedly recommended 

 by experience, if we simply compare together facts under the most 

 widely differing forms which they can assume, and exclude all 

 those which merge into one another, as must be done in every 

 artificial mode of division. A simple microscopical examination of 

 these croupous exudations shows that the object which we are here 

 considering is not pure fibrin, for even in the most recent forma- 

 tions the microscope reveals, in addition to a fibrous substance 

 not very unlike freshly coagulated fibrin, a great number of mole- 

 cular granules and flake-like laminae, which at certain spots appear 

 to be jagged. After they have existed for a longer time, we ob- 

 serve in them nuclei and cyto'id corpuscles ; indeed the occurrence 

 of the latter is often so sudden (or in other words the metamor- 

 phosis of the solid exudation into pus-corpuscles is so rapid) that 

 many observers have altogether doubted the previous separation 

 of fibrin. The questions which have been propounded to chemists 

 since Rokitansky's original subdivision of the various kinds of 

 fibrin, are in part solved by microscopical investigation. The 

 substance to which Rokitansky applied the term croupous or 

 aphthous fibrin, or which he regarded as the primary matrix differ- 

 ing from ordinary fibrin is now in a great measure found not to be 

 fibrin at all ; and he himself has noticed the absence of that net- 

 work of fibres which is peculiar to coagulated fibrin both in the 

 aphthous coagulum and in the croupous exudation ft. These granu- 

 lar solid exudations are no longer fibrin, having undergone various 

 chemical as well as morphological metamorphoses before they come 

 under our notice. One might, indeed, here assume, as has been 

 done, the existence of a dimorphism, such as has been shown in 

 recent times to exist in the case of many mineral substances ; but 

 independently of the fact, that true heteromorphism is far less 

 frequent in organic chemistry, and that its existence in respect to 

 fibrin still remains undetermined, the qualitative chemical investi- 

 gation of these exudations shows us that the granular matter which 

 they contain is by no means chemically identical with the unaltered 

 fibrin which is often still contained in these deposites. 



In those exudations, which Rokitansky names aphthous,, we 

 find, after careful washing, no material which, after the exudation 



