Menstruation

The monthly change in the mucous membrane of the uterus, which accompanies the discharge of the ovum.

Meroblastic

The form of ova in which the yolk does not undergo complete segmentation, as that of birds.

Mesencephalon

Those parts of the brain developed from the middle cerebral vesicle, viz , crura cerebri and corpora quadrigemina.

Mesoblast

The middle of the three layers of the blastoderm from which the connective tissues and vascular apparatus of the embryo are formed.

Metabolism

The intimate chemical changes occurring in the various organs and tissues upon which their nutrition and functions depend.

Metanephros

The hinder portion of the Wolffian body which develops into the kidney and ureter.

Metazoa

A term used to denote all those animals whose ova undergo division, in contradistinction to Protozoa.

Methaemoglobin

A compound formed by oxyhaemoglobin combining more firmly with additional oxygen.

Micrococcus

An extremely minute fungus of a round shape. Micrococci occur in many solutions of decomposing organic matter.

Micturition

The act of voiding urine.

Molecules

The smallest physical particles of matter that can exist in a separate state. They are probably always constituted of two or more atoms. Morphology. The science which treats of the forms and structures of living beings.

Morula

The stage of development of the ovum after segmentation, in which all the young cells are alike, before the blastoderm is formed.

Mucin

The characteristic constituent of mucus.

Mullerian Duct

An embryonic structure from which are formed the genital passages in the female, viz., Fallopian tube, uterus and vagina.

Mydriasis

A dilated state of the pupil.

Myograph

An instrument for graphically recording muscle contraction.

Myopia

The condition in which the focus of parallel rays of light falls short of the retina; short sight.

Myosin

The substance formed by the coagulation of muscle plasma. It is one of the globulins.

Natural Nerve Currents

The electrical currents passing through an exposed muscle or nerve while in a state of rest.

Neuroglia

The reticular connective tissue which binds together the elements of the nerve centres.

Non-Polarizable Electrodes

Electric terminals specially constructed so as not to set up secondary currents on application to moist living tissues.

Notochord

The primitive vertebral axis of the embryo.

Nucleolus

A small spot observable in some nuclei.

Nucleus

A central part of a cell differentiated from the main protoplasm, commonly round, but sometimes elongated, as in muscle.

Odontoblasts

Living cells lining the pulp cavity of the interior of a tooth, and presiding over the growth and nutrition of the dentine.

Olfactory

Pertaining to the sense of smell.

Omphalo-Mesenteric

The vessels connecting the embryonic circulation with the yolk sac, which are early obliterated in the mammalian foetus.

Ophthalmoscope

An instrument consisting of a small mirror, by which the interior of the eye can be illuminated so that the fundus may be viewed.

Optic Cup

The involuted optic vesicle which is developed into the retina, etc.

Osteoblast

The active cells in forming bone.

Osteoliths

Calcareous particles lying in the endolymph.

Oxyhaemoglobin

The coloring matter of the blood corpuscles.

Paraglobulin

One of the more abundant albumins of the blood - serum globulia.

Paramcecium

A unicellular organism composed of a soft mass of protoplasm enclosed in a firmer case, and covered with motile cilia.

Parapeptone

A body produced in gastric digestion during the formation of peptone.

Pepsin

A ferment existing in the gastric juice which converts proteids into peptones.

Peptone

A form of albumin which is produced during the digestion of proteids; it is very soluble, and diffuses readily through a membrane.

Perilymph

The liquid surrounding the membranous labyrinth of the ear.

Peristalsis

The mode of contraction of the muscular walls of certain tubes as the oesophagus and intestine, the effect of which is to cause a progres sive constriction, and so force the contents of the tube onward.

Phakoscope

An instrument for estimating the changes in the shape of the lens during accommodation, by doubling the reflected images with a prism.

Placenta

The intra uterine organ by means of which the foetal blood is brought into close relationship to that of the mother, so as to gain nutriment and oxygen, and get rid of effete matters.

Plasma

A term meaning anything formed or moulded; used in physiology to indicate chemically complex kinds of matter which subserve to the formation of the living tissues.

Poikilothermic

Varying in temperature. A term applied to those animals whose temperature varies with that of the surrounding medium - "coldblooded animals".

Presbyopia

A loss of power of accommodation for near vision which accompanies old age.

Prosencephalon

That part of the developing anterior cerebral vesicle from which are formed the olfactory and optic lobes, the hemispheres, and corpora striata and optic thalami.

Protista

A large group of organisms which remain in the primitive state of a single cell during their lifetime.

Protococcus

A unicellular vegetable organism, the protoplasm of which contains chlorophyll.

Protoplasm

The substance which gives rise to the primitive vital phenomena, seen in unicellular organisms, and which is the chief agent in executing the functions of all the active tissues.