342 EPITHELIAL AND ENDOTHELIAL TISSUE. 



at first solid in other words, the bioplasson is in the juvenile 

 condition. Later, the solid bioplasson divides into a reticulum, 

 with, in the center, solid masses, termed nuclei. At the periphery 

 the cement-substance is formed, though this, owing to the pres- 

 ence of the connecting filaments (" thorns"), never completely 

 separates the single endothelia into individual cells. Thus, the 

 wall of the capillary, even after the formation of endothelia, 

 remains a continuous layer of bioplasson, endowed with con- 

 tractility and with the capacity of growing, especially in the 

 inflammatory process. In retrogression of the capillaries the 

 hollow bioplasson is first solidified, then breaks up into medul- 

 lary elements and gives rise to connective tissue, from which, 

 under all circumstances, the capillaries have originated. 



Th. Schwann * found in the germ-membrane of the ovum of the chicken, 

 thirty-six hours after hatching, cells which, by elongation in different direc- 

 tions, became stellate. He called these cells the cells of capillary vessels, 

 and considered the blood-corpuscles as young cells formed in the cavity of 

 the capillary vessel cells. 



C. Rokitanskyt knew that in certain morbid processes, especially in the 

 growth of cancer, blood originates in cells which had become tubular or club- 

 shaped. The prolongation of the cells he considered as a beginning new for- 

 mation of blood-vessels. He also maintained that a so-called insular new 

 formation of blood took place in the process of inflammation. 



S. Strieker t asserted that the capillary tube is a hollowed out protoplasma 

 endowed with many of the characteristics of life ; that a solid thread, first 

 simply an offshoot of a capillary vessel, afterward becomes hollow ; that in 

 the tail of the tadpole there are vessels filled with colored blood-corpuscles, 

 terminating at either end in the shape of extremely delicate solid processes. 



E. Klein demonstrated that in the germinal disk of the chicken embryo, 

 in the first half of the second day of hatching, some elements of the middle 

 germinal layer exhibit vacuoles. These vacuoles, he asserted, were the first 

 formations of blood-vessels, and that from its protoplasmic walls masses are 

 separated, partly colored and partly colorless the blood-corpuscles. In 

 other cells of the same germinal layer, occasionally multinuclear, he observed 

 in the center an endogenous formation of blood-corpuscles, while the peri- 

 phery of the cell was transformed into the endothelial wall of the vessel. 



My own researches || have resulted in the conclusion that living proto- 

 plasma, in the condition termed "hsematoblastic," viz. : in a juvenile con- 

 dition of development, is the material from which originate both the colored 

 blood-corpuscles and the wall of the blood-vessels. 



* " Mikroskopische Untersuchungen," etc., 1839. 



t "Handbuch der Allg. Patholog. Anatoinie," 1846. 



\ "Studien iiber den Ban und das Leben der capillareii Blutgefasse." Sitzungsber. d. 

 Wiener Akad. d. Wissensch., 1865. 



" Das mittlere Keimblatt in seinen Beziehungen zur Entwicklung der ersten Blutgefasse 

 u. Blutkorperchen im Huhnerembryo." Sitzungsber. d. Wiener Akad. d. Wisaensch., 1871. 



||"Ueber die Kiick-u. Neubildung von Blutgefassen im Knochen u. Knorpel." Wiener 

 Medls. .Tahrbiiclier, 1873. 



