length as the erythrocyte but somewhat narrower. The nucleus is round,
stains purple with the Wright’s stain, and the chromatin material is
somewhat diffused. The diameter of the nucleus is nearly equal to that
of the cell. The cytoplasm is pale and may show vacuoles near the
nucleus. They may contain small circumscribed red structures. They vary
somewhat in size and shape. There are in the domestic fowl between
45,000 and 55,000 per cubic millimeter.
=Leucocytes.=—There are, in the blood of the hen, 28,000 to 35,000
leucocytes per cubic millimeter. The leucocytes may be divided into five
distinct types. These are as follows:
_Polymorphonuclear leucocytes_ with eosinophilic rods (Fig. 74, No. 2)
are round and have a diameter about equal to the length of the
erythrocyte. The nucleus is polymorphous; that is, it has two or more
lobes. The nucleus stains a pale blue, and the chromatin is diffused.
The cytoplasm is colorless with bright red staining spindle-shaped rods.
There are 28 to 32 per cent. of this type of cell in the blood of the
hen.
[Illustration:
FIG. 74.—Blood cells of the fowl. _Wright’s stain._ From a S. C. Rhode
Island Red cockerel. 1, Basophile (mast cell) with lilac staining
spherical granules. 2, Eosinophile with rod-shaped acidophile
bodies. 3 and 4, Eosinophiles with acidophile staining round
granules. 5, Eosinophile ruptured. 6, Mononuclear leucocyte with
vacuoles in the cytoplasm. 7 and 9, Transitional leucocytes (first
stage). 8, Mononuclear leucocyte. 10, 11, and 12, Small lymphocytes.
13 and 14, Large lymphocytes. 15, A lymphocyte. 16, Lymphocyte
(nucleus centrally located). 17 and 18, Transitional leucocyte. 19,
Thrombocyte. 20, Neutrophile (polymorphonuclear). 21, Erythrocytes.
]
Polymorphonuclear leucocytes with eosinophilic granules (Fig. 74, No. 3
and 4) are of about the same shape and size as the preceding. The
nucleus is similar to the former except that it may appear slightly
picnotic. The cytoplasm stains not at all or faintly blue; it contains
round or spherical granules which stain a dull red. There is from 4 to 6
per cent. of this type of eosinophiles found in the domestic fowl.
_Lymphocytes_ are round in shape and of about the diameter of the width
of a thrombocyte (Fig. 74, No. 11). The nucleus is round, staining
somewhat purple, and contains a diffused chromatin material. The
cytoplasm exists in only small amounts; it lies to the side of the
nucleus and stains a pale blue. This is the small lymphocyte. A similar
cell but much larger also exists. This is the large lymphocyte (Fig. 74,
No. 13). There is from 40 to 44 per cent. of the lymphocytes in the
blood of the fowl. The small lymphocytes are most abundant.
_Large mononuclear cells_ (Fig. 74, No. 6) either round or oval, in
shape, whose diameter may be about that of an erythrocyte and at times
much larger. The nucleus may be round, oval, or irregular, and at times
rather crescent or U-shaped (Fig. 74, No. 17). The cytoplasm is abundant
and completely surrounds the nucleus. The cytoplasm stains a paler blue
than the nucleus. Both taking the basic stain as do the lymphocytes.
These constitute 18 to 20 per cent. of the cells of the blood.
_Mast cells_ or _basophiles_ (Fig. 74, No. 1) are of about the same size
and shape as the eosinophiles. The nucleus is round or oval, and stains
a very pale blue. The cytoplasm is colorless, mostly to one side of the
nucleus, and contains round or spherical purple staining granules. This
type of cell constitutes from 2 to 4 per cent. of the white cells of the
blood.
=Structure of the Red Blood Cell.=—The red blood cell is composed of a
spongy stroma holding in its meshes the red coloring matter. The stroma,
or framework, of the erythrocyte consists principally of nucleo-albumin;
it contains lecithin, cholesterin, and salts. The red matter consists of
an albuminous crystalline substance called hemoglobin, which forms about
90 per cent. of the total solid matter of the dried corpuscle. Each red
cell offers a certain absorbing surface for oxygen. As the blood
circulates through the delicate walls of the lungs and the air-sacs, it
takes up oxygen; the blood at the same time delivers to the air carbon
dioxid which has been brought from the tissues where active cell
metabolism has been going on. This oxygen taken up by the erythrocyte
forms a loose chemical union and is known as oxy-hemoglobin. In this
form it is carried to the tissues of the body where it is given up by
the erythrocyte to the tissues where oxidation is going on.
_Hemoglobin_ is a crystallizable proteid substance containing carbon,
hydrogen, oxygen, nitrogen, sulphur, and iron.
=Formation of the Cells of the Blood.=—The red blood cells are formed in
the red marrow of the bone.
Polymorphonuclear leucocytes are formed in the red marrow of the bones,
and the lymphocytes in the lymph glands and lymph follicles.
The bird carries a normal body temperature of 105° to 107° F. The
average temperature of 50 mature hens and cocks was 106.8° F. The blood
is of a deep red color.
=Composition of the Blood.=—The average composition of the blood of the
domestic fowl as given by Owen, is as follows:
Whole shed blood:
Water 780 parts
Clot 157 parts
Albumin and salts 63 parts
—————
1000 parts
Moist blood cells:
Average total weight 456.69
Water 342.52
Solid matter 97.50
Plasma:
Total weight 543.30 parts
Water 495.72 parts
Solid matter 30.72 parts
Blood when drawn and allowed to stand soon coagulates. In the blood of
birds this process is very rapid, the blood coagulating, in most
instances, in about one-half minute. Blood coagulates only in the
presence of calcium salts.
During life, the liquor sanguinis is termed plasma; but after it has
been shed from the body and coagulation has taken place, the liquid
residue is called serum. Serum is plasma with its modifications as the
result of coagulation, and as this latter process is brought about by
the production of fibrin, we may say that serum is plasma minus
fibrin-forming elements.
The proteids of the serum are serum globulin, serum albumin, and a
ferment produced as the result of coagulation. As fibrinogen is used up
in the process of coagulation, it is not found in the serum, but there
is in the serum a proteid known as fibrino-globulin. This is produced
from fibrinogen during the process of fibrin formation. The following
tabulation gives a clear idea of the difference between the proteids of
plasma and of those of serum:
Proteids of Plasma
Fibrinogen
Serum globulin
Serum albumin
Proteids of Serum
Serum globulin
Serum albumin
Fibrin ferment (nucleoproteid)
Fibrino-globulin
Fibrinogen is the precursor of fibrin.
The fibrin of the blood clot of the bird is soft and very lacerable. The
serum is usually yellow.
THE FATE OF THE ERYTHROCYTE OF THE FOWL
The power of vascular endothelium to ingest red blood corpuscles has
been studied by Keys.
When bacteria or other minute foreign bodies are injected into the blood
stream of pigeons, they are rapidly withdrawn from the circulation into
the tissues of the liver and of the spleen. The foreign bodies are noted
to be contained within cells of a distinct type, which is found in both
liver and spleen. This type of cell contains, in addition to the foreign
substances injected, much yellow pigment, and when tested for iron by
Pearl’s method gives a positive Prussian-blue reaction.
In such specimens there is a display of contrast to other tissues. There
is an extensive content of cells possessing the distinct tone of
Prussian-blue iron reaction. These cells are distributed rather evenly
throughout both the spleen and the liver, but more numerously in the
liver.
In the liver, under low-power magnification, these cells appear as blue
patches, sharply differentiated from the red-stained parenchyma. These
cells are larger in their greater diameter than the liver cells. They
vary much in size and form. They bear a constant relationship to the
venous capillaries, and often appear to occupy the lumen of the vessels.
Under higher magnification it is noted, however, that each cell is an
integral part of the endothelial intima lining of the capillaries. They
are therefore fixed tissue cells, engaged by one of its surfaces upon
the reticulum of the vessel wall, with a free surface bulging a greater
or less degree into the lumen of the vessel. The attached surface of the
cell follows exactly the line of the vessel wall. These cells are
similar to those described for mammals by Kupffer and are called Kupffer
cells or stellate cells. In the fowl Keys proposes the name hemophages.
The nucleus of the hemophage stains a deep garnet with the carmine used
in the above-given technic, and contains two or three very distinct and
intensely stained nucleoli. In the hemophages, which are more nearly
flat, the nucleus appears like those of the typical endothelial cells;
whereas in the protruding hemophages of greater bulk, the nucleus is
more vesicular and is irregularly pyramidal in form. Rarely two nuclei
are found in one cell. Within this cell may be seen vacuoles of the
cytoplasm which contain red blood corpuscles. These blood corpuscles
have been phagocyted from the circulating blood stream. Approximately
one-third of the intimal cells are hemophages. Each hemophage displays
evidence that it contains, or has recently contained, one or more red
blood cells. The cell body of the hemophage has no fixed morphology, but
changes from time to time according to its phase of phagocytic activity.
In a stage which the hemophage has recently ingested a red blood cell,
the cell body bulges out into the lumen of the vessel and the nucleus is
crowded to one side. At this time the red blood cell appears as those in
the blood stream and possesses the characteristic staining reactions.
The nucleus of the red blood cell stains deep reddish brown and the
cytoplasm an even yellow bronze. In the next stage the cytoplasm of the
hemophage gives a diffuse Prussian-blue reaction. Then in hemophages
which represent later stages there are various stages of disintegration
and digestion of the red blood cell. The first changes of the phagocyted
red blood cell is hemolysis, the hemoglobin escaping into vacuoles of
the cytoplasm of the phagocytic cell, leaving the nucleus-containing
stroma distinctly outlined. The stroma may retain the original ovoid
form or may become spherical; the nucleus in such instances remains
ovoid. Gradually, both the stroma and nucleus lose their staining
reaction until finally the vacuoles contract about a small indistinct
remnant of the nucleus, which in its turn ultimately disappears. During
this latter process the size of the hemophage gradually decreases. The
hemoglobin, which has escaped into the cytoplasm of the hemophage, is
seen to undergo a series of changes. At first the greater part of the
pigment does not give the iron reaction but retains its yellow-bronze
tone with erythrosin and occupies vacuoles of various sizes. Later the
contents of the vacuoles give the iron reaction and with increasing
intensity. Later there is a gradual decrease in the staining reaction
indicating that the iron gradually disappears from the cells which
extracted it from the red blood cells it digests. As a summary we find,
that these cells take care of the worn out red blood cells. They devour
them; hemolyze them, destroying the stroma and nucleus; split the
hemoglobin and free the iron; and then finally return to their normal
form.
The spleen contains the same type cells, but they are fewer in number.
For the most part they are confined to the pulp cords and have no such
evident relation to the vessel wall, or lumen, as in the liver.
The function of the cells of the spleen are essentially the same as
those in the liver.
Iron freed from the worn out red blood cells is not retained by the
cells freeing it, nor is it found in the bile. It does not occur
elsewhere in the tissues of the liver and spleen. It is possibly
discharged into the blood stream, and transported to the hemapoietic
tissues. Cells which hemolyze red blood cells and liberate the iron are
to be seriously thought of in connection with bile formation since
bilirubin is approximately, if not identical with, iron-free hematoidon.
NEUROLOGY
=The Nervous System.=—The nervous system is an apparatus by means of
which animals appreciate and become influenced by impressions from the
outer world. Animals react on these impressions, and thus are enabled to
adapt themselves to their environment. This system is the organic
substratum of life, sensation, and motion. Broadly stated, the nervous
system connects the various parts of the body with each other, and to
coördinate the parts into a harmonious whole in order to carry on the
bodily functions methodically and to control the physiological division
of labor throughout the organism.
The nervous system consists of two parts. The first is the
_cerebro-spinal system_, which comprises the central nervous axis,
including the brain and the spinal cord, and the peripheral nerves,
including the cranial and the spinal nerves. The second is the
_sympathetic nervous system_. The two parts of the system are closely
linked together, and both terminate in peripheral nerve endings,
including those of special sense, of sensation, and of motion.
The cerebro-spinal nerves especially preside over the special senses,
motion and sensation; and the sympathetic over the digestive, the
pulmonary, and the vascular apparatus.
From a structural standpoint, the nerve system consists of cell elements
peculiarly differentiated from all other tissue cells in that their
protoplasm is extended in the form of processes, often to great
distances from the nuclear region. The cell elements are held in place
by supporting tissue and receive an abundant blood supply; they are
partly of ectodermal and partly of mesodermal origin.
The cell element of the nerve system, called a _neurone_, is the
developmental, structural, and functional unit of the nervous system. It
is a single cell presenting unusual structural modifications. It
comprises not only the nerve cell body with its numerous protoplasmic
processes, or dendrites, but also the axone, which may vary in length
from a fraction of a millimeter to fully half the bird’s length. The
bulk of the axone is many times the bulk of the cell body.
Certain non-medullated axones are surrounded by a delicate, homogeneous,
nucleated sheath, called the neurilemma, or sheath of Schwann.
THE CRANIAL NERVES
The cranial nerves have their origin in the brain and leave the cranial
cavity in pairs. They are numbered numerically from before backward,
there being twelve pairs in all. The following is a tabulation according
to their number, name, and function:
No. Name Functional Nature
I. Olfactory Smell-sense
II. Optic Visual-sense
III. Oculomotor Motor to muscles of eyeball and orbit
IV. Pathetici Motor to superior oblique muscle of eyeball
V. Trifacial Mixed: Sensor to face and tongue. Motor to face
VI. Abducentes Motor to External rectus of eyeball
VII. Facial Motor to muscles of head and face
VIII. Auditory Hearing-sense
IX. Glosso-pharyngeal Mixed: Tongue, pharynx and muscles of throat
X. Vagus Mixed: Sensori-motor to respiratory tract and part of alimentary tract
XI. Spinal accessory Motor to muscles of pharynx, neck and heart
XII. Hypoglossal Motor to muscles of the tongue
=Olfactorius.=—Nervus olfactorius (Fig. 75, _C_, 16). This is the nerve
of smell, one of the nerves of special sense. The organ of smell
consists of five layers as follows:
First, a layer of olfactory fibers extending in different directions and
consisting of a dense plexiform arrangement of the axones of the
olfactory cells. From this layer the fibers pass into the layer of
olfactory glomeruli where their terminal ramifications mingle with the
dendritic terminals of cells lying in the more dorsal layers, to form
distinctly outlined spheroidal or oval nerve fiber nests, the _olfactory
glomeruli_.
Second, a fine granular layer of basic substance containing round
cellular structures, the _stratum granulosum_.
Third, broader granular, or molecular layer, having on its inner surface
a row of large pyramidal cells which are both small and large and which
send their dendrites into the olfactory glomeruli. Their points are
directed outward.
Fourth, a layer of round cells tightly pressed together and measuring
about 5 microns in diameter. Between these cells are very fine nerve
fibers.
[Illustration:
FIG. 75.—The brain of a hen. Photograph.
_A._ Upper surface of the brain. 1, Medulla oblongata. 2, Calamus
scriptorius. 3, Cerebellum. 4, Optic lobes. 5, Transverse fissure.
6, Longitudinal fissure. 7, Upper surface of the left cerebral lobe.
8, Upper surface of the right cerebral lobe. 9, Lateral pillar of
the cerebellum.
_B._ The posterior surface of the eyeball. 10, The sectioned surface
of the optic nerve.
_C._ The inferior surface of the brain. 11, Corneo-scleral juncture.
12, The cornea. 13, The sclera. 14, The optic nerve. 15, The optic
chiasm. 16, The olfactory lobes. 17, The medulla oblongata. 18,
Tuber cinererum et infundibulum.
]
Fifth, a layer of epithelial cells.
The peripheral fibers and the nerve cell layers near the hemispheres
disappear so that the basic substance of the trabecula with the
hemispheres form the entire lobe mass. On the lower surface of the
hemispheres there is a long bundle of nerve fibers which enter into the
substance of the olfactory lobes and there disappears. These fibers are
medullated. Non-medullated fibers enter into the makeup of the olfactory
trunk.
The original center of the olfactory nerve is not in the hemisphere, but
in the same location as the optic nerve. This nerve trunk consists of
very fine non-medullated fibers. The nerves of smell are therefore not
peripheralistic nerves. The nerve fibers are distributed to the mucous
surface of the turbinated bones. Toward the front they form an expanded
prolongation.
The olfactory nerve, as it emerges from the cone-like anterior tip of
the cerebrum, is of considerable thickness and extends along with the
median dorsal artery of that region above and to the inside of the
orbit, under the thin bony structure. Before its termination into the
posterior turbinated bones, it is crossed by the superior maxillary
division of the fifth pair of cranial nerves. It extends as far as the
pituitary membrane of the turbinate bones upon which its filaments are
distributed radially.
=The Opticus.=—The nervus opticus (Fig. 75, No. _C_, 14) the second
cranial, is the nerve of sight. The optic lobe, or tuberculum bigeminum
lies at the base of the brain on each side of the optic tract.
From the optic lobes the two trunks pass forward along the under surface
of the cerebri, forming the optic chiasm at the hypophysis (Fig. 75, No.
_C_, 15), at which point the nerve fibers originating from the right
side pass to the left, and _vice versǎ_. From the chiasm the true optic
nerves pass forward to the posterior surface of the eyeball. They are
composed of a bundle of very fine, marrow-like nerves. These fibers
enter into the ganglionic cells of the retina. By removal of the finely
adherent neurilemma, the optic nerve is seen to be composed of parallel,
longitudinal lamellæ, the margins of which are mostly free on one side.
=The Motor Oculi.=—The motor oculi (Fig. 62, No. _C_, 10), the third
cranial nerve is a motor nerve. It originates close to the base of the
brain behind the position of the hippocampus of mammals on the inner
side of the crus cerebri, and also on the inner somatic column close
below and somewhat aside from the aqueduct of Sylvius. The nerve leaves
the brain cavity through a distinct foramen near the foramen opticum,
and supplies the following eye muscles: first, after entering the orbit,
it sends a branch upward to the inferior portion of the inferior rectus;
then, it gives off the thick ramus ciliaris. The trunk then extends
under the optic nerve and passes forward to innervate the inferior
rectus, the internal rectus, and the inferior oblique. A ciliary
ganglion forms on the trunk.
=The Patheticus.=—(Fig. 62, No. _C_, 11) is a small motor nerve,
originating close to the sulcus centralis, in the circle of the center
brain over the valve of Vieussens, between the posteriors of the optic
lobes. It extends in a dorsal direction between the cerebellum and the
lobus opticus, to the posterior of the latter of which it then forms a
loop ventrally. Lying close to the optic foramen it passes through a
fine opening into the eye cavity and supplies the superior oblique
muscle of the eye. During its course it passes dorsally over the optic
nerve, and then crosses dorsally over the ophthalmic division of the
fifth pair of cranial nerves and the internal rectus muscle.
=The Trifacialis.=—(Fig. 62, No. _C_, 12). This, the fifth cranial, is a
mixed nerve and is divided into two parts, portio major and portio
minor.
The _portio major_ originates in the ganglion cells of the posterior
part of the brain. Commencing near the medulla oblongata it passes
through the posterior part of the brain, then upward and outward; and
along its route it forms the Gasserian ganglion, which lies partly in
the cranial cavity or in its wall.
The _portio minor_ consists of the downward passing fibers containing
the motoric elements which are distributed to the muscles of the jaw and
of the eye. The roots are found in the ganglion from the center and back
brain, close below the pathetic nerve origin, where the pathetic passes
between the lobus opticus and the pars peduncularis; it then takes a
lateral course between the two.
The fibers of the portio minor do not take part in the formation of the
Gasserian ganglion, but are only partly surrounded by it.
There are three nerve trunks given off of the trifacialis: the
ophthalmic, the superior maxillary, and the inferior maxillary.
The _ophthalmic division_ of the fifth nerve is the smallest of the
three branches. It emerges directly from the Gasserian ganglion, and
passes through a narrow bony canal in the base of the brain, below the
pathetic and the abducens, and through the foramen ophthalmicum. It then
enters the eye cavity above the optic nerve, and on the wall of the
cavity extends downward, and with regard to the eyeball, dorsally lying
close to the rectus internus muscle and close to the surface of the
eyeball. It passes along the olfactory nerve, extends under the superior
oblique muscle, and finally reaches the inner angle, or canthus, of the
eye. It here divides into the recurrent externa and the ethmoidalis. The
ethmoidalis branch is a straight continuation of the ophthalmic. It
extends along close to its fellow of the opposite side, and, over the
vomer, splits into two branches. The smaller of these branches breaks
through the bone cells of the jaw, continues upon its ventral surface in
a furrow extending forward, and terminates in the gum region. It
supplies the gum and point of the beak. The larger branch enters into
the cell substance extending to the tip of the beak, in its course
sending out a number of fine filaments, which spread out along the outer
surface. At this point these two branches may fuse. The larger branch is
endowed with the sense of touch.
The recurrent externa divides shortly after leaving the main trunk of
the eye cavity passes over the lacrimal gland. It gives two branches to
this gland and one to the membrana nictitans, and innervates the upper
eyelid. It then emerges from the eye cavity, passing over the os
lacrimale, and gives one or more branches to the integument of this
region, including the comb. This branch is large in birds with a large
comb. Branches pass in front of the lacrimal bone through the outer
nasal cavity and into its deeper structure.
Shortly after the ophthalmic branch has entered into the eye cavity and
before it crosses the optic nerve, it gives a fine branch to the motor
occuli.