CONNECTIVE TISSUE IN AMPHIBIA 461 



Innerhalb der einmal angelegten Intercellularsubstanz wachsen die 

 Bindegewebsbimdel spaterhin selbstandig weiter fort, in die Lange 

 sowohl in die Dicke. Dasz das Langenwachstiim ohne eine besondere 

 Tatigkeit der Zellen vor sich geht, ist wohl immer angenommen worden ; 

 was das Dickenwachstum anlangt, so war friiher die Anschaimg viel- 

 fach verbreitet, dasz die Zellen neue Fibrillen auf die Oberfliiche der 

 erstmals angelegten Bimdel abscheiden. Indessen ist dies niir eine For- 

 mel, welche zwar aiis dem cellularen Prinzip sich ergibt, aber immoglich 

 iiberall zutreffen kann. Tatsache ist, dasz man im lockeren Binde- 

 gewebe die Zellen oft nur sehr sparsam eingestreut findet, und dasz 

 die Bindegewebsbimdel auf weite Strecken bin mit ihnen in keiner 

 Berlihrimg stehen, also nur durch eigene Assimilation wachsen konnen. 



Heidenhain further holds^^ that the living intercellular material 

 is of a more passive nature, in fact a sort of a living framework 

 which lacks many of characteristics of true cell cytoplasm, but 

 still retains at least for a time the power of growth through 

 intussusception, and the ability to differentiate new fibrillar 

 structures. To quote: "Die Metaplasmen sind in Verhaltnis 

 zu den eingeschlossenen Zellen eine lebende Substanz besonderer 

 Art, welche in eine andere Bahn der Entwickelung iibergegangen 

 ist, ohne dasz eine Moglichkeit der Riickverwandlung in Proto- 

 plasma besteht." 



The adoption of this view of a living exoplasm wdth the power 

 to assimilate food material and the ability to differentiate new 

 fibrillar structures independently of the typical cells at once 

 raises a number of questions. In the first place this living exo- 

 plasm must be regarded, as stated by Heidenhain, as being of 

 a lower grade of living matter than that found in the regular 

 cell bodies. It possesses only certain of the vital activities and 

 entirely lacks others. In other words, it is necessary to conclude 

 that, in the connective tissues of an animal, there are different 

 degrees of living matter, beginning with the nucleus of the cell 

 as the highest type, then grading into the endoplasm of the cell 

 bodies and finally into the common exoplasm. 



In the second place, the postulation of a living exoplasm 

 modifies the cell theory to a great extent, and delegates many 

 of the powders supposedly possessed only by cells to masses of 

 intercellular material, in considerable areas of which even nuclei 



" Hpidenhain, 1907, p. 48. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 28, NO. 3 



