CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 19 



is to say, that some of the larger migratory cells have originated from 

 a branched cell. In negative silver preparations of a corresponding 

 young nodule it can he made out also that the clear lymph-cana- 

 Hcular system contains not only the network of branched cells, but 

 also the migratory cells. Besides the latter, we find also larger 

 isolated nodules in the fenestrated part of the omentum ; they are 

 already provided with a system of capillary blood-vessels. As regards 

 their minute structure, one can determine with certainty in positive 

 silver preparations that their matrix is occupied by more or less 

 flattened cells, which, in the same way as in the rabbit's omentum, are 

 the more branched the nearer they are to the borders of the nodules. 

 In negative silver preparations we find the lymph-canalicular system 

 accordingly so transformed that in the central parts of the nodule 

 the lacunae communicate with each other only by a few short cana- 

 liculi or even touch each other in lines ; whereas in the peripheral 

 parts of the nodule the number and the length of those canaliculi 

 become greater. We need only add that from those more or less 

 branched cells of the matrix migratory cells may be seen to grow 

 up like knobs and become separated. 



Besides the nodules just mentioned, we find also here, especially in 

 the pleura mediastini of the cat, smaller nodules of an elongated shape, 

 which consist of a delicate reticulum of nucleated branched cells, the 

 meshes of which are perfectly filled with lymphoid corpuscles. 

 Finally, we find nodules, and shorter or longer tracts, which possess a 

 very rich system of capillary blood-vessels. Between these capillary 

 blood-vessels extends a reticulum of pretty large branched cells, the 

 meshes of which are either perfectly clear and empty, viz. contain 

 nothing but fluid, or they contain here and there a smaller or larger 

 lymphoid cell, which in some instances may be seen to grow up from 

 those branched cells, viz. we find in one place that from a branched 

 cell of the reticulum a nucleated rounded knob projects into the 

 space of an adjacent mesh ; and not far from that we find a similar 

 appearance, with this difference, that the nucleated knob is raised 

 from its branched cell by a more or less deep furrow. In a third 

 case we find the nucleated knob previously mentioned connected with 

 the branched cell by means of a thin peduncle. From these facts we 



c 2 



