EPITHELIAL AND ENDOTHELIAL TISSUE. 341 



silver staining, and the capillary appears as a continuous layer of 

 bioplasson, which here and there is slightly thickened. This 

 becomes comprehensible through the facts taught by the history 

 of development of the capillary blood-vessels. 



Nerves have often been demonstrated in the walls of capil- 

 laries by means of gold-staining. They appear as a delicate, 

 beaded retieulum, running in the cement-substance, in the same 

 manner as in epithelia. (See page 324, Fig. 140.) 



Peculiar vascular formations are the coccyyeal and carotid "glands" and 

 the plexus choroidei. They are composed of convolutions of capillary blood- 

 vessels, with vesicular club-shaped or semi-globular prolongations, in connec- 

 tion with the caliber of the capillary. Neither the coccygeal nor the carotid 

 gland are epithelial or glandular formations, therefore the word u gland" is a 

 misnomer in this connection. C. Langer discovered in the mucosa of the palate 

 and throat of frogs semi-globular prolongations of the capillaries, often with 

 anastomosing the caliber of the capillary by means of a narrow pedicle. He 

 considers these formations equivalent to capillary loops. 



Development of Capillaries. S. Strieker (1865) first proved that 

 the capillaries are originally solid strings, either connected with 

 the wall of an already formed capillary, or representing solid, 

 club-like outgrowths from this wall. These solid strings become 

 afterward excavated, vacuoled, and the originally solid wall of 

 the capillary is differentiated finally into endothelia. 



My own researches corroborate this discovery of Strieker. I 

 have seen solid, club-shaped formations in the middle of a 

 medullary space, which were new formations produced by the 

 retrogression of cartilage tissue to its embryonal condition. (See 

 page 246.) I also have observed that the originally solid club or 

 cord-like formations become vacuoled even before a connection is 

 established with older blood-vessels, and that in the vacuole 

 unchanged masses of bioplasson remain, which I have called 

 haematoblasts, because they are the future blood-corpuscles. I 

 made similar observations in the study of the process of inflam- 

 mation in different varieties of connective tissue, all of which go 

 to prove that a capillary is originally a solid mass of bioplasson, 

 which by vacuolation becomes hollowed, while some particles of 

 bioplasson are furnished with haemoglobin, and converted into 

 colored blood- corpuscles. In 1873, I said that wherever a trans- 

 formation of one tissue into another takes place, either as a 

 normal process, or as the result of inflammation, a new forma- 

 tion of blood-vessels and blood-corpuscles invariably occurs as a 

 part of the process. The wall of the newly formed capillary is 



