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The fluid is lashed rhythmically by these fibers, and a spiral movement of the utmost grace results. Then do the intermediate forms that move also possess these flagella, and does this least form in nature, viz., Bacterium termo, accomplish its bounding and rebounding movements in the same way?

If any of the smaller species, especially Bacterium termo, are brought to rest, and then introduced into a fluid in which there is the minutest trace of free oxygen, they will immediately begin to move about freely; and if the oxygen is gradually introduced, their motion will be set up only in those parts of the drop which the oxygen reaches.

This instrument is so constructed that it appears to throw the image of the object upon the white sheet of paper on the small table at the right hand where the drawing is made, at the, same time that it enables the same eye to see the pencil and the right hand. In this way I made a careful drawing of B. termo and its flagellum, magnified 5,000 diameters. Here is a projection of the drawing made.

The objects therefore are all equally magnified, and their relative sizes may be seen. The giant of the series is known as Spirillum volutans; and you will see that the representative species given become less and less in size until we reach the smallest of all the definite forms, and known to science as Bacterium termo.

The phenomena are as massive and wide-spread as is anything in Nature, and the study of them is as tedious, repellent and undignified. To reject it for its unromantic character is like rejecting bacteriology because penicillium glaucum grows on horse-dung and bacterium termo lives in putrefaction. Scientific men have long ago ceased to think of the dignity of the materials they work in.

But the point of difficulty was B. termo. The demonstration of its flagella was a task of difficulty which only patient purpose could conquer.

There was the bacillus anthracis; there was the micrococcus; there was the Bacterium termo, and the Bacterium lactis that's what turns the goat milk sour even to this day, Hare-Lip; and there were Schizomycetes without end. And there were many others...."

I have stated that they were the inevitable accompaniments of putrescence and decay. You learned from a previous illustration the general appearance of the Bacteria; they are the earliest to appear whenever putrefaction shows itself. In fact the pioneer is this the ubiquitous Bacterium termo. The order of succession of the other forms is by no means certain.

If it were measured it must be by an indirect progress, which I accomplished thus: The diameter of the body of B. termo, i.e., from; side to side, may in different forms vary from the 1/20000 to the 1/50000 of an inch. That is a measurement which we may easily make directly with a micrometer.

See lib. ii. cap. 34: 'Nel nostro scrivere non intendiamo far giudizio delle cose incerte, e massimamente della intenzione e animo segreto degli uomini, che non apparisce chiara se non per congettura e riscontro delle cose esteriori. E però stando termo il primo proposito, vogliamo raccontare quanto più possibile ci sia, la verit