GLOSSARY. 727 



Decidua vera. The altered mucous membrane of the uterus, which 

 lines that organ during gestation. 



Deglutition. The act of swallowing. 



Desquamation. The term used to denote the casting off of the 

 outer layer of the skin. 



Dialysis. The diffusion of soluble crystalloid substances through 

 membranes such as parchment. 



Diastole. The period of relaxation and rest of the heart's muscle. 



Dicrotism. The double wave of the arterial pulse. The dicrotic 

 wave is seen on the descending part of the pulse curve. 



Dioptric media. Transparent bodies, such as those parts of the 

 eye which so refract the light that images come to a focus on 

 the retina. 



Distal, A term used to denote a part relatively far from the centre. 



Ductus arteriosus. A short bond of union between the pulmonary 

 artery and the aorta, which, in the foatus, carries blood from the 

 right side of the heart into the aorta. 



Ductus venosus. A vessel which, in the foetus, carries blood from 

 the umbilical vein to the vena cava. After birth it becomes a 

 fibrous cord. 



Ductus vitello-intestinalis. The union between the yolk sac and 

 the intestine of the embryo. 



Dyspnoea. Difficulty of breathing ; it is a condition in which inor- 

 dinate respiratory movements are excited by an unusually ven- 

 ous state of the blood in the respiratory nerve centre. 



Ectoderm. The outer layer of simple organisms. 



Ectosarc. A term applied to certain unicellular organisms, mean- 

 ing the outer layer or covering. 



Electrodes. The two terminals which are applied to a substance 

 in order to complete the circuit when it is required to pass a 

 current through the substance. 



Electrotonus. A peculiar electric state of nerves resulting from the 

 passage of a continuous current through them. 



Embryo. The name given to the animal at the earliest period of its 

 development. 



Emmetropic, A term applied to the normal eye, in which parallel 

 rays of light are brought to a focus at the retina without accom- 

 modation. 



Emulsification. The suspension of very fine particles of liquid or 

 solid in a liquid which is not able to dissolve them. 



