458 GEORGE A. BAITSELL 



connective tissues. In such cases it was possible to observe all 

 stages in the process from an apparently homogeneous ground 

 substance or matrix to the heavy fibrous tissue. By the use of 

 a microscope equipped for dark field illumination it was possible 

 to analyze the transformation process and to demonstrate that 

 the fibers arose as a result of a fusion and consohdation of the 

 minute elements of the fibrin clot which under ordinary illumi- 

 nation were entirely invisible. In experiments of this type, 

 inasmuch as cells were not present, it was possible to state with, 

 absolute certainty that the fibers had arisen through a modifi- 

 cation of the ground substance of the clot. 



In other types of experiments with plasma clot preparation 

 in which cells were present, it was shown ('15) that a trans- 

 formation of the clot, and consequently fiber formation, could 

 be brought about by mechanical factors induced by the move- 

 ments of the cells through the clot. A case of this is shown in 

 figure 5^ which is a drawing of a portion of a plasma clot prepara- 

 tion at a magnification of 950 diameters in which a piece of 

 muscle tissue had been imbedded. A spindle-shaped cell has 

 left the piece of imbedded tissue and is moving through the fibrin 

 clot. In this preparation, the path of the cell can be traced 

 from the imbedded tissue through the clot to its present position, 

 by means of the fibrillar structure' which has arisen in its wake 

 in the ground substance of the clot. In this and similar cases it 

 is clear that the fiber formation in the clot has taken place by 

 the introduction of mechanical factors through the cell move- 

 ments with a consequent fusion and consolidation of the minute 

 elements of the fibrin clot. 



In figure 6 is shown a portion of a transverse section through 

 the tail region of a 75 mm. embryo of R. catesbiana at a magnifi- 

 cation of 75 diameters. In this embryo the connective tissue 

 is more mature in type with a practically complete transformation 

 of the ground substance into a fibrous tissue. It will be noted 

 in the figure that the densest formation of connective tissue is 

 in the region immediately surrounding the notochord and also 



5 Baitsell, 1915. A photomicrograph of this preparation is published in this 

 paper as fig. 19. 



