THE CONNECTIVE TISSUES 99 



ing a reticulum. The fibrils present much the same microscopic 

 appearance as the white fibres of areolar tissue. Also in certain 

 organs, e.g., the lymph nodes, the direct continuity of the fibres of the 

 coarser fibrous tissue of the trabeculoe with the fibrils of the reticular 

 tissue can be easily demonstrated. In some locations, e.g., in the 

 lymph nodes (Fig. 47) the cells of the reticular tissue lie upon the 

 surface of the fibrils and so completely invest them that the fibrillar 

 character of the tissue cannot be seen until the overlying cells have 

 been removed. This has led to two views regarding the relations 

 between the cells and fibres of reticular tissue, one that the relation 

 is the same as in other forms of connective tissue, the cells lying on 

 the fibres but being entirely separate from them, the other that the 

 fibres run through the protoplasm of the cells. This view considers 

 reticular tissue a less dift'erentiated type than fibrous tissue, develop- 

 ment having stopped at a point where the cells (fibroblasts) still have 

 fibrils running through their protoplasm. 



Reticular tissue has been described as yielding on boiling, a sub- 

 stance called by some elastin by others reticulin instead of gelatin 

 which results from boiling fibrous tissue. Other recent studies upon 

 the chemistry of reticular tissue are not however in accord with this 

 view, reticular tissue being found to yield gelatin on boiling. Both 

 tissues resist pancreatic digestion, and the question as to the structural 

 and chemical relations of the two tissues remains at present unsettled. 



Reticular connective tissue forms the framework of adenoid 

 tissue and of bone-marrow. It is also present in large amounts in 

 the spleen and in the mucous membrane of the gastro-intestinal 

 tract, lung, liver, kidney, and other organs where it forms the 

 finer part of the framework, supporting the capillaries, and often 

 apparently serving as a basement membrane for the gland cells. 



TECHNIC 



I. Areolar Tissue, to show White and Elastic Fibres. — Remove a bit of the 

 subcutaneous tissue, as free from fat as possible, from a recently killed animal. 

 Place it upon a mounting slide and with teasing needles quickly spread it out in 

 a thin layer. During this manipulation the specimen should be kept moist by 

 breathing on it. Put a drop of sodium chlorid solution upon the specimen and 

 cover. 



As the specimen is unstained, a small diaphragm should be used for the micro- 

 scopic examination. 



The white fibres are straight or wa\y, are crossed in all directions, and are 

 longitudinally striated. The elastic fibres have been stretched and show as 

 sharp lines with curled ends where the fibres are broken. 



