absorbs carbonic acid and gives off oxygen. It can be proved that the carbonic acid is decomposed; that the decomposition is due to the disrupting energy supplied by the sunlight; that the instrument by which the sunlight is thus annihilated as such, is the green plant matter chlorophyll. For every molecule of plant substance that is made then, there is absorbed by the plant a certain quantity of sunlight energy; and the difference between plant protoplasm and animal protoplasm lies in the fact that the former has a powerful servant, chlorophyll, which is able to convert the wave motion of light, which directly of itself is useless to the vegetable protoplasm into chemical energy capable of tearing to pieces stable bodies like carbonic acid and building out of their residues complex structures. We may metaphorically speak of the metallic circuit of an electric lighting apparatus as the plant substance, the electric current as the sun's energy and the tiny carbon or platinum thread as the chlorophyll by means of which that energy is converted into another and useful form.

If there be this essential identity in the structure and functions of all living matter, the proper method of arriving at a true conception of the nature of these in the most complex individual is to study first the simplest body in which they are manifested.

An example of such a simple organism is furnished by the living white blood corpuscle; still better by a tiny inhabitant of stagnant water, known as the amoeba. This is a microscopic colorless mass with a firm hyaline border and a more fluid granular interior.

Watch it under the microscope and the amoeba is seen to be nearly continually in motion; now there projects from one side an extemporized arm of its body substance and into this flow the contents of the animal, the opposite border of the animal following the motion, and this change of form and place occurs indifferently in any direction. The motion bears no resemblance to that tremulous movement which all finely divided inorganic particles have in a fluid-the so-called Brownian movement. It bears no likeness to the stretching and relaxation of a rubber band. It is true contractility.

Our amoeba is nearly continually in motion, whether it moves or not or what direction it follows cannot possibly be predetermined; so this living speck possessed the wonderful property of spontaneity; which is simply a term to indicate change without apparent cause.

If by proper means you pass an electric shock through the amoeba all its processes are drawn in and the creature becomes a rounded, motionless mass. Or if in its wanderings it strikes against an obstacle, it immediately turns off in another direction where the path is free. The amoeba then possesses irritability through the excitement of which it attains a sensation of contact.

When one part of the living mass is excited in this way, the result shows that the stimulus has permeated the whole body of the animal; it possesses therefore conductivity.

None of these properties could be of use to the creature if it existed alone. In order that the perception of external conditions should be of use and that the contractions should be of avail, the motion of every part of the body must have a purposeful relation to that of every other part. That is the case, and the animal possesses the power of coordination by which one concrete activity is realized from the fusion of many separate

ones.

Such a body as this when it comes upon a piece of matter good for food throws its body round and engulfs it, and now this food is chemically changed from its former condition of plant or animal matter and becomes to a greater or less extent amoeba stuff. This process of making a foreign body like itself is assimilation and assimilation leads to an increase in size of the amoeba, or growth.

Inanimate objects may also increase in size as a crystal or a snow-ball rolled over the snow. But in these cases the growth is by accretion; each new particle is laid in a definite layer on the outside of those already deposited.

When a living organism grows, however, it increases throughout its whole thickness, the new molecules find their way equably between those in the uttermost parts of the structure. This is growth by intussusception. In the same sort of way you get an equable mixture of two gases, like oxygen and nitrogen when they are put into the same vessel one on the top of the other.

As a matter of observation you know that the growth of any living organism has its limit; and the reason is plain. It requires expenditure of energy to effect changes in food matter taken in to build it up to a higher chemical level; such energy must in the end be produced at the expense of the substance of the amoeba itself, leading to a chemical degredation of part of it; this broken down part is no longer fit for working material; it is waste matter and must be cast out.

Now the amount of food taken in must depend upon the absorptive surface of the amoeba, while the amount of chemical changes effected and consequently the weight of waste matter depends upon the mass of the animal.

It is well known that when a body, like a sphere, increases in size its surface increases as the square of its diameter while its mass increases at the cube of the same; hence in our amoeba a point is sooner or later reached where the mass is so great compared to the absorptive surface, that the weight of egesta resulting from chemical change in tissue and food matter just balances that of the ingesta.

But this living creature has a remarkable way of circum

venting, as it were, this limitation to its growth, and it is to this property that the propogation of the species is due. When the amoeba has been well fed and is under favorable conditions, its nucleus elongates, as does the whole body of the creature. The nucleus begins to pull itself apart into halves; the general amoeba substance behaves in the same manner. Little by little this separation becomes more complete till, finally, we have complete division and two new ameobæ as the result of it, each of which begins its new life by feeding and growing as did its parent.

Finally, this living protoplasm has some peculiar power of self-protection in regulating the nature of substances that shall diffuse into it. Put a living amoeba into a staining fluid and its body remains colorless, the dissolved pigment cannot penetrate it. As soon as the creature is dead, however, the color passes into and stains it deeply.

The higher animal body exists at first as an egg, a single cell with more or less of the characters described as pertaining to the amoeba. But most animals have a developmental history in which the original cell by division gives birth to multitudes of others and these separate into unlike groups and thus differentiated become the bases of the various tissues of the body. The cells which thus come to make up the adult tissues look very differently among themselves. They are usually made up of a granular protoplasm in which is imbedded a nucleus with nucleoli and each may be surrounded by a distinct cell membrane.

During development more or less matter is laid down as a bed between them, so that this cellular and intercellular matter makes up and characterizes every part of the body.

Now as with development there proceeds a differentiation of tissues, there is at the same time a physiological division of labor in the body; so that the fundamental properties spoken of above are not now all performed to the same extent by every part but are restricted, this function to one, that to another organ or tissue. The advantage of this specialization to the perfection of the whole working organism is obvious.

That community is savage and of little social influence in which every man is sufficient unto himself; where he is his own butcher, carpenter and shoemaker. On the other hand, civilization becomes more perfect and the community more powerful, the more minutely these different tasks are distributed among special individuals. In the same way the bodily organism becomes of a higher order and more efficient in every way, as the energies of various organs are directed into narrow and special channels. An animal tissue, like a man, may do one thing well but many things poorly.

We can then make a physiological classification of tissues which corresponds tolerably well with the anatomical one,

though not perfectly, for one tissue may have more than one distinct physiological property.

Classified thus we can call our tissues by certain few physiological names which designate their properties, and in this way we can distinguish more or less definitely the following

groups:

Undifferentiated tissues.-Including, embryonic cells; lymph and white blood corpuscles; many connective tissue corpuscles. We call them undifferentiated, not because each of these bodies may not have special hereditary proclivities, but because we cannot recognize any preponderant function pertaining to them.

Supporting tissues.-Cartilage; bone; connective tissue.
Nutritive tissues.-These fall into several subdivisions:

(1) Assimilative: a, secretory; glands; b, receptive;
digestive tract.

(2) Eliminative or excretory; skin; lungs; kidney.
(3) Respiratory; red blood corpuscles; lungs.

(4) Metabolic; tissues which are more distinctly the seat
of chemical changes which go to sustain the body at
large; liver. More or less a character of all active
tissues.

Storage tissues.-Liver; fat. A general character of all tissues to some extent.

Irritable tissues.-Recipients of impressions from the outside world. The sense organs and nerve endings.

Conductive tissues. Also irritable. They transmit impulses
generated in the foregoing. Nerves.
Coordinating and automatic tissues.-Nerve cells.
Motor tissues.-Cilia; striped and unstriped muscle.
Protective tissues.-Skin; hair; nails; bone.

Reproductive tissues.-Ovary; testicle.

No matter how specialized any tissue may be, we shall see that it is in continual physiological connection with all the rest of the body; and every change that goes on in it must make itself felt, to a greater or less degree, by every other tissue.

THE AMBULANCE HOSPITAL FOR SMALL-POX.*

BY HENRY F. LYSTER, A. M., M. D.

Professor of Principles and Practice of Medicine, Michigan Medical College.

At the close of a recent sanitary convention in Flint, those members who had come from a distance when about taking the train for their homes, were thrown into some consternation by the chairman of the convention, who had reserved his fire to send this parting shot: "You have all come here," he said, "and we have been delighted to meet you. You have *Read at Sanitary Convention held at Ann Arbor, March 1, 1882.

called our attention to numberless sources of disease and death, but you have not told us how to detect and correct them. You have spoken of the danger to health from poisonous wells, but you have given us no simple tests by which we can detect impure water. You have spoken of the evils entailed by want of drainage and sewerage, but you have given us no plan by which we may proceed to drain and sewer our homes, under conditions which obtain at our residences whether in villages or on farms."

These sanitary conventions, if they are to be productive of the greatest good, are not intended to be merely suggestive and theoretical, but they must be practical, and while the awakening of the people to the great truths of sanitary science is of the first importance, the ready application of these truths to their every-day life and modes of living should immediately follow so far as it is possible to make them do so.

We have all heard recently a good deal about small-pox, and are all aware that every few years the disease seems to get a foothold, as it were, in the State, and appears here and there, usually on some of the great thoroughfares of travel.

Small-pox has been present at every port of emigration in Europe during the past year, and consequently it has been largely imported and spread far and wide in our own country by emigrants. Fortunately we can boast the enlightenment which has made our people appreciate and practice a very general vaccination, and it is to this fact solely that we are spared to-day a pestilence which otherwise would be decimating our people.

I have the official reports of the Registrar of Vital Statistics, Dr. Baker, which show how insignificant the proportion of small-pox has been during eleven years in this State, from 1869 to 1879 inclusive:

While scarlet fever and diphtheria have been very formidable, and the latter has been particularly alarming in its progressive increase from year to year, small-pox has only within the past six months become of more than ordinary interest, and is, owing to a very general vaccination, not likely to prevail to any great extent, but on the contrary will undoubtedly rapidly diminish, if not entirely disappear. It is necessary, how