152 H. E. JORDAN AND K. B. STEELE 



Zimmermann ('10) and his students, Palczewska ('10) and Wer- 

 ner ('10). It is the purpose, in part, of this investigation to 

 present further facts in support of the non-cellular interpreta- 

 tion of vertebrate heart muscle. 



Marceau ('04) states that he was unable to demonstrate discs 

 in the heart muscle of vertebrates lower than birds; 1 also in goose 

 and duck. Moreover, he says that discs develop only some time 

 after birth. The further object of our research is to test the 

 factual basis of these assertions and to determine, if possible, 

 from structural marks, the probable function of the intercalated 

 discs. 



II. MATERIAL AND METHODS 



The material studied includes heart muscle of adult human, 

 monkey, sheep, bat, cat, guinea-pig, mouse, rabbit, chipmunk, 

 opossum, humming-bird, lizard, turtle, toad, frog and trout; also 

 of guinea-pig of last week of gestation, and of first, second, third 

 and fourth weeks of post-natal life; of a cat embryo of four days, 

 and of a four-year-old child; and of Limulus. 2 



Zimmermann's technic 3 was employed except for adult human, 

 cat, rabbit, sheep and lizard hearts. Mammalian cardiac muscle 

 of the latter group has been fully described and illustrated by 

 Werner. We shall confine our descriptions for the most part 

 to the heart muscle of forms not previously studied. The 

 descriptions in every instance apply to the ventricular tissue. 



1 In the second volume (1911) of 'Plasma und Zelle,' Heidenhain says 

 'Schaltstticke wurden bisher in keinen Falle bei niederen Wirbeltiere beobachtet; 

 sie findcn sich by Vogeln zum ersten Male.' 



2 We are indebted to Messrs. H. F. Jackson and E. L. Powers for kindly col- 

 lecting the material of toad, frog, trout and Limulus at Cold Spring Harbor, L. I. ; 

 and to Dr. W. H. Schultz, of the Hygienic Laboratory, Washington, for the young 

 and foetal guinea-pig hearts. 



3 Following this technic, small pieces of tissue were treated for twenty-four 

 hours with a solution of 90 parts of absolute alcohol plus 10 parts of 25 percent 

 HN0 3 . The tissue was then washed in several changes of 94 per cent alcohol or 

 until the latter remained neutral to litmus paper. It was then passed into dis- 

 tilled water, from which it was transferred to a solution of 1 gram of Griibler's 

 haemalum in 10 cc. of water. Here it remained for from eight to ten days when it 

 was washed in distilled water and then carried through the ordinary steps of the 

 paraffin technic. In our own experience we have obtained equally successful 

 preparations by staining sections for twenty-four hours on the slide. 



