bo 
Emil Goetsch. 
the one hand, and the number and size of the csophageal glands 
on the other hand. For example, Ranvier (84), speaking of the dif- 
ference between the rodents and the dog in this respect, remarks 
that this is easily comprehensible when one remembers that in the 
rabbit and other rodents the bolus of food is liquid or semi-liquid, 
and therefore mucous glands are not necessary, that on the other 
hand the dog swallows greedily solid matters and untriturated bones 
and hence the glands are indispensable. Renaut (97) similarly calls 
attention to the difference in masticatory efficiency between the ox 
and rodents on the one hand and the dog on the other and explains — 
on this basis the differences in the number of cesophageal glands. 
Many examples can be found in favor of this explanation. When, 
however, one attempts to give it a general application, unexpected 
difficulties arise. For example, there is not a sufficient difference 
in the development of the salivary glands, of the masticatory mech- 
anism, or in the consistence of the food, to explain adequately the 
fact that glands are very numerous in the cesophagus of the dog and 
wholly absent from that of the cat. 
The possibility that the mechanical function of the cesophageal 
glands may be a purely subsidiary one, and that their true function 
may be something quite different from this, has received but little 
attention at the hands of the investigators. Rubeli (90), it is true, 
suggested that the secretion might be of use in digestion, but his 
suggestion was based not on experimental data derived from mam- 
mals but on the observations of Decker (87), Swiecicki (76), Lang- 
ley (79), ete, on the formation of proteolytic enzymes in the 
cesophagus of fishes and batrachians. As will appear later, these 
observations deal with structures which are not homologous with 
the cesophageal glands of mammals and can therefore not be used to 
draw conclusions concerning the function of the mammalian cesoph- 
ageal glands. In this connection a question of much importance which 
has been variously answered by different observers is whether the 
esophageal glands of mammals are pure mucous glands, or mixed 
glands containing serous demilunes. If serous cells are present, 
then one must at once think of a chemical function of the esophageal 
secretion as well as a mechanical one. Klein (79) asserts that 
