OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 87 



In order to investigate this point, I made gold preparations of 

 muscle taken from the Rat's heart. The cells are seen to contain a 

 network similar to that of ordinary striped muscle. The network is 

 more delicate and with much smaller meshes than the network in 

 the body-muscle of the same animal, and is therefore more difficult 

 to demonstrate by the gold method (Fig. 9). I have also prepared 

 muscle from the heart of the Frog (Fig. 10) and Bird (Fig. 11) ; the 

 network in the latter animal is much plainer than in the others. 



The striation of cardiac muscle therefore appears to he due to an intra- 

 cellular network similar to that of ordinary striped muscle. 



Unstriped Muscle of Vertebrates. 



Klein* describes in the unstriped muscle of vertebrates a bundle 

 of longitudinal fibrils which are in connection with the intranuclear 

 network. His description of the structure of the unstriped muscle- 

 cell is as follows : " Thus we may regard the unstriped muscle- 

 fibre as composed of a sheath with annular thickenings and a bundle 

 of delicate fibrils which at one more or less central point forms a 

 delicate network. This, surrounded by a special membrane— except 

 where the network is in connection with the bundle of fibrils — 

 represents the nucleus." Klein regards the bundle of fibrils as the 

 contractile part of the cell, and thinks that by their shortening the 

 muscle-fibre is caused to contract, elongation being produced by the 

 elastic rebound of the sheath. Flemmingf has observed these 

 fibrils in the living muscle. 



Dr. Klein informs me that he regards the bundle of longitudinal 

 fibrils as representing an intracellular network homologous with 

 other intracellular networks. Dr. Klein has been kind enough to 

 show me his preparations of unstriped muscle prepared from the 

 mesentery of the newt by twenty-four hours immersion in 5 per 

 cent, ammonium bichromate, and afterwards stained with logwood. 

 These preparations show clearly the longitudinal fibrils and their 

 connection with the intranuclear network. 



I have made preparations, by the gold method, of muscle from the 



* Klein, "Atlas of Histology," p. 74, pi. xv. ; also "(Mart,. Journ. Micr. Sci.," 



1S78. 



i « Beobachtungen ittjer die Beschaffenheit des Zell Kerns," "Arch, fur Mikr. 

 An.it," 1876, Bd, xiii., pp. 714, 715. 



