336 LUCILE WITTE 
To return to Jordan’s paper on the humming-bird, he gave 
fourteen very conclusive points as to why he thought the inter- 
calated discs could not be cell boundaries. One point which 
seemed very readily to contradict the cell-boundary theory was 
that he had found discs which lay over the nucleus. They 
usually were peripheral in the fiber, and they also varied to a 
great extent in coarseness—a condition which is not common to 
cell walls. As has been stated, Jordan concluded from his four- 
teen observations that intercalated discs were not cell walls or 
cement lines. As to the function of the discs, he only conjec- 
tured. They might have something to do with contraction, 
since they were found in patches and much more numerous in 
contracted than in relaxed fibers. His figures, however, failed 
to prove his statement that the dises were more numerous in 
contracted than in relaxed areas. Figures 2 and 4 represented 
discs in contracted fibers, while figures 1 and 3 represented 
normal areas of the fiber. According to these, there were not 
as many discs in contraction (fig. 4) as in relaxation (fig. 1 and 3). 
Figures 1 and 2 might easily be explained as discs occurring in 
normal relaxed fibers. 
Up to the time of writing his paper, Jordan had not found 
discs in fetal hearts. This would seem to disprove any idea 
that the discs were related to the rhythmic beat of the heart. 
His final conclusion was that the discs ‘‘were of the same nature 
as the anisotropic bands, were closely related to them in position, 
and might represent a definite physiologic or functional state.” 
H. E. Jordan and K. B. Steele* in 1912 worked out a com- 
parative study of vertebrate hearts in which they attempted to 
show that intercalated discs were to be found in animals lower 
than birds and also in fetal material. In this they succeeded, 
for they were able to demonstrate discs in amphibians (frogs 
and toads), reptiles (turtles and lizards), and fishes (trout), and 
in the fetal guinea-pig hearts during the last week of gestation. 
The technic used was Zimmermann’s. The discs in the fetal 
hearts appeared simultaneously with the striations and increased 
in number with the growth of the animal after birth. The discs 
were also found to be present in a cat embryo of four days. 
