through which the blood leaves the liver; _d d_, the
position of the liver cells between the meshes of the capillaries; _A A_,
branches of the hepatic artery to the interlobular connective tissue and
the walls of the large veins and large bile ducts. These branches are seen
at _r r_ and form the vena vascularis; _v v_, vena vascularis; _i i_,
branches of the hepatic artery entering the substance of the lobule and
connecting with capillaries from the interlobular vein. The use of the
hepatic artery is to nourish the liver, while the other vessels carry blood
to be modified by the liver cells in certain important directions; _g_,
branches of the bile ducts, carrying bile from the various lobules into the
gall bladder and into the intestines; _x x_, intralobular bile capillaries
between the liver cells. These form a network of very minute tubes
surrounding each ultimate cell, which receives the bile as it is formed by
the liver cells and carried outward as described.

Fig. 2. Isolated liver cells: _c_, blood capillary; _a_, fine bile
capillary channel.

PLATE V. Ergot in hay: 1, bluegrass; 2, timothy; 3, wild rye; 4, redtop.
Ergot is a fungus which may affect any member of the grass family. The
spore of the fungus, by some means brought in contact with the undeveloped
seed of the grass, grows, obliterates the seed, and practically takes its
place. When hay affected with ergot is fed to animals it is productive of a
characteristic and serious affection or poisoning known as ergotism.

PLATE VI. Ergotism, or the effects of ergot. The lower part of the limb of
a cow, showing the loss of skin and flesh in a narrow ring around the
pastern bone and the exposure of the bone itself.

* * * * *

POISONS AND POISONING.

By V. T. ATKINSON, V. S.

[Revised by C. DWIGHT MARSH, Ph. D.]

DEFINITION OF A POISON.

To define clearly the meaning of the word "poison" is somewhat difficult.
Even in law the word has never been defined, and when a definition is
attempted we are apt to include either too much or too little. The
following definition given by Husemann is perhaps the best: "Poisons are
those substances, inorganic or organic, existing in the organism or
introduced from the outside, produced artificially or formed as natural
products, which, through their chemical nature, under definite conditions,
so affect some organ of a living organism that the health or well-being of
the organism is