288 H. E. JORDAN AND J, B. BANKS 



tate the silver nitrate. Observations are recorded below which 

 indicate that the j^recipitation of silver nitrate within the discs 

 is incidental to the presence of tissue-fluid in the interstices of 

 the fundamental bacillary elements of the discs, which fluid has 

 penetrated via the telophragmata from the tissue spaces between 

 the fibers. In myocardium treated with silver nitrate the telo- 

 phragmata also precipitate the salt and appear more deeply 

 colored. The ready passage of tissue-fluid along the telophragma 

 is provided for by the close union between telophragmata and 

 sarcolemma. 



The three most widely prevalent hypotheses above discussed 

 meet \vith such serious objections when thoroughly analyzed and 

 strictly applied that they must be abandoned as complete inter- 

 pretations of the intercalated discs. It will be the chief burden 

 of this new investigation to further support the hypothesis first 

 suggested by Jordan and Steele (14) that the discs are of the 

 nature of irreversible contraction bands. The suggestion had 

 frequently been made by various investigators that the inter- 

 calated discs are related in some manner to contraction phe- 

 nomena, but their specific interpretation as modified irreversible 

 contraction bands had not been previously proposed. 



II. HISTOLOGIC METHODS 



The tissues were in every case fixed in the nitric-acid-alcohol 

 mixture of Zimmermann (24). Parallel series of sections were 

 prepared according to Zimmermann's hemalum-staining method, 

 and with the iron-hematoxylin-van Gieson combination. Disso- 

 ciated tissues were also prepared for study by maceration with 

 potassium hydroxid, and staining on the slide with a dilute 

 solution of methylene blue. Ventricular tissue was treated also 

 with silver nitrate solutions for study of possible intercellular 

 cement. Beautiful and most instructive preparations were made 

 also by teasing hemalum-stained blocks of tissue, and mounting 

 the fragments in glycerin on the slide. This last technic may 

 be very highly recommended as a simple routine laboratory 

 method for class demonstration of intercalated discs. Not only 



