The Cilium. 201 



that it is coniijoscd of fibrillae and interfibrillar substance. However 

 they may have arisen, they are a fact in the structure and not an 

 ■^Accident of structure,' as Biitschli maintains. In every case in 

 which I have studied contractile tissue it has been comj^osed of 

 fibrillae or a single fibril running out from a cell." 



Discussion of Results. 



Present authorities are perhaps about equally divided on the ques- 

 tion of the fibrillar, alveolar or colloidal-fluid nature of contractile 

 protoplasm. In the cilium we have this most interesting substance 

 in not only its purest, but also its simplest form. It is thus the 

 natural point from which to begin the study of its structure ; and by 

 taking advantage of the natural path afforded by a comparative series 

 of typical cilia, it seems possible to gain clearer conceptions than those 

 attained through any other line of approach. The general conclusion 

 is that contractile protoplasm is fibrillar in all the forms studied. 



The fibrillar structure is preserved in its normal appearance by but 

 few of the ordinary killing reagents. The great majority so alter 

 the fibrillae that they are no longer recognizable. This fact goes far 

 toward explaining the confusion in current ideas of protoplasmic 

 structure. Before we deny fibrillar structure in any tissue we clearly 

 must determine whether the reagent used preserves fibrillae. The 

 beginning which has been made in my investigation of the effects of 

 killing reagents on cilia leads us to conclude that osmic acid alone 

 can be depended upon to preserve fibrillae in their normal appearance. 

 Anyone who will watch cilia dissolve or change into granujes during 

 a second's contact with an unfavorable reagent will require no fur- 

 ther argument on this point. ISTaturally, some fibrillae are more 

 resistant than others. Thus, the fibrillae in the pseudopods of 

 Actinosphaerium were left intact by reagents which completely de- 

 stroy their identity in the cilia of Stylonychia. 



A point of special importance is the result gained by teasing 

 flagella fresh under high powers of the microscope. Structures re- 

 vealed by this method arc in no wise open to the criticism that they 

 are artifacts produced by killing reagents. The ease with which the 

 flagella studied are resolved into their component fibrils and the clear- 



