THE ADRENAL SECRETION AND THE HEART. 433 



THE ACTION OF THE ADRENAL SECRETION AND THE OXIDIZING 

 SUBSTANCE UPON THE CARDIAC MUSCLE. 



The histology of the myocardium still offers a broad field 

 for conjecture, notwithstanding the many investigations to 

 which it has been submitted by modern observers. The known 

 facts are briefly these: Its tissue is composed, in man, of 

 short, round fasciculi, or 'bundles, of striated fibers, possessed 

 of thick lateral projections. The latter directly connecting 

 with a similar projection of the adjoining bundles and being 

 cemented to it, a thick close-meshed net-work is formed: a 

 characteristic of the heart-muscle. But it differs from other 

 muscles in several other particulars; its fibers are one-third 

 smaller and their striae are much more faint; they possess no 

 sarcolemma and are, therefore, exposed to the immediate action 

 of a fluid that may surround them. The manner in which 

 the contractile structures are combined in bundles is also 

 peculiar: each bundle is made up of central prismatic fasciculi 

 of round fibers, in which nuclei (one or two) with their sur- 

 rounding protoplasmic area are imbedded, the whole being 

 surrounded with flat or ribbon-like columns of muscle-fibers. 

 The perinuclear protoplasm referred to generally contains fat- 

 droplets and minute pigment-granules which resemble haemo- 

 globin, and sends projections between the surrounding mus- 

 cular fibers so that each of the latter is connected with and 

 is only separated from its neighbor by a layer of protoplasm. 

 This arrangement does not in any way modify the manner in 

 which the sarcous elements are disposed, while the disks, clear 

 spaces, etc., are precisely as they are elsewhere in the organ- 

 ism. These muscular "primary" bundles form, by their union 

 with one or two of their neighbors, columns, or chains or 

 "secondary" bundles, which are covered, as shown by Ranvier, 

 with a sheath of loose connective-tissue cells, which cells, in 

 turn, connect with one another by numerous projections, or 

 extensions. The primary fasciculi also contain connective- 

 tissue sheaths which invest the muscle-fibers and are likewise 

 supplied with connective-tissue cells. All this forms a close, 

 though permeable, net-work, which makes it possible for a 

 liquid to penetrate the muscular columns or chains and come 

 into direct contact with the bare, or exposed, muscle-fiber. 



