$2 HISTOLOCY OF THK POISON-GLANDS OF 13 UFO AfiUA. 



The acinus of the mature gland is, in good preparations, found entirely full of the 

 poison which is the toad's means of defense against attacks of an enemy. In the mature 

 gland acinus one can see that the undischarged poison is of two sorts, which occupy definite 

 and different positions in the lumen of the acinus. This is especially evident in glands 

 which have just reached the mature stage. In the center of the acinus the great mass of the. 

 secretion is granular and contains numerous globular bodies, some! imes gathered into masses, 

 the so-called "poison grains." About the walls of the gland acinus, however, is a layer of 

 material, very different in character, which has a perfectly homogeneous appearance, 

 always distinct and easily seen, no matter how old the mature gland. Such layers of gland- 

 content differ not only in appearance, but are also chemically distinct. In sections of 

 material fixed in Orth's or Cohn's fluid, or like mixtures, the ehromaffin reaction occurs in 

 the homogeneous layer. In other words, the epinephrin content of the toad venom is in 

 the clear homogeneous liquid part of the gland "secretion," which is found lying next the 

 gland-wall. 



If we examine the wall of the mature poison-gland, having epinephrin in its lumen, with 

 the higher powers of the microscope, we see a very curious picture. We have said above- 

 that the epinephrin is found about the periphery of the gland acinus. Such an examination 

 discloses the fact that the secretion is not walled off by the matrix which bounds the cavity 

 of the sac. but that the homogeneous epinephrin-containing fluid extends out into the 

 muscular layer surrounding the gland, filling in the spaces between the muscle-fibers and 

 running between them in all directions, like an injection mass. This probably is the result 

 of pressure unavoidably exerted on the glands when preparing them for fixation, since the 

 same appearance may be seen, though not in as great a degree, in glands recently discharged 

 by normal contraction of the muscular layer of the gland-wall. It is an interesting comment 

 on the nature of the matrix in which the cells of the muscular layer are embedded, showing 

 as it does that the matrix probably exists in life as a gel which allows free change in shape 

 of the muscle-fibers during contraction. In contraction during the normal expulsive act, 

 the swelling of the muscle-fibers and their compression into a smaller space probably result 

 in the formation of a firm wall which prevents backing up of the fluid in the gland under 

 pressure. 



As the gland grows older, unused after reaching maturity, diffusion takes place and t he- 

 whole content of the gland becomes infiltrated with the chromate-reducing epinephrin- 

 containing liquid, so that after treatment with chromate mixtures the entire gland-content 

 hits a yellow stain, but the liquid layer is always distinguishable- by its clear, homogeneous 

 appearance and by its more intense ehromaffin reaction. 



The significance of this may be readily understood when we e-onsider the physiology of 

 the expulsion of the glandular secretion when the toad is stimulated in any way, e. </., by 

 seizure by an enemy. ( 'ontraction of the muscular layer about the gland causes first a dila- 

 tation of the duct lumen and an opening of the acinus. This preliminary dilatation is proba- 

 bly due to the contraction of the muscles about the gland-collar and the adjacent portion of 

 the acinus. Immediately following the dilatation of the duct, or coincident with it, strong 

 contraction of the muscles encircling the entire acinus empties the duct completely. The 

 very thick, compact corial layer probably serves as a support about the duct, preventing its 

 dilating under the strain of the pressure exerted by the strongly contracting muscles, so 

 that the original size of the duct lumen is retained throughout. Thus the liquid gland secre- 

 tion may spurt in a jet onto the oral mucous membrane of the animal which has seized t he- 

 toad. When considerable pressure is applieel to the glands, the se-cretion may be shot or 



