But in my opinion we can now be assured sufficiently that no animals, however small they may be, take their origin in putrefaction, but exclusively in procreation... For seeing that animals, from the largest down to the little despised animal, the flea, have animalcules in their semen, seeing also that some of the vessels of the lungs of horses and cows consist of rings and that these rings can occur on the flea's veins, why cannot we come to the conclusion that as well as the male sperm of that large animal the horse and similar animals, and of all manner of little animals, the flea included, is furnished with animalcules (and other intestines, for I have often been astonished when I beheld the numerous vessels in a flea), why, I say should not the male sperm of the smallest animals, smaller than a flea may even the very smallest animalcules have the perfection that we find in a flea.

I have destroyed almost the whole race of frogs, which does not happen in that savage Batrachomyomachia of Homer. For in the anatomy of frogs, which, by favour of my very excellent colleague D. Carolo Fracassato, I had set on foot in order to become more certain about the membranous substance of the lungs, it happened to me to see such things that not undeservedly 1 can better make use of that (saying) of Homer for the present matter—
'I see with my eyes a work trusty and great.'
For in this (frog anatomy) owing to the simplicity of the structure, and the almost complete transparency of the vessels which admits the eye into the interior, things are more clearly shown so that they will bring the light to other more obscure matters.

It is the destiny of wine to be drunk, and it is the destiny of glucose to be oxidized. But it was not oxidized immediately: its drinker kept it in his liver for more than a week, well curled up and tranquil, as a reserve aliment for a sudden effort; an effort that he was forced to make the following Sunday, pursuing a bolting horse. Farewell to the hexagonal structure: in the space of a few instants the skein was unwound and became glucose again, and this was dragged by the bloodstream all the way to a minute muscle fiber in the thigh, and here brutally split into two molecules of lactic acid, the grim harbinger of fatigue: only later, some minutes after, the panting of the lungs was able to supply the oxygen necessary to quietly oxidize the latter. So a new molecule of carbon dioxide returned to the atmosphere, and a parcel of the energy that the sun had handed to the vine-shoot passed from the state of chemical energy to that of mechanical energy, and thereafter settled down in the slothful condition of heat, warming up imperceptibly the air moved by the running and the blood of the runner. 'Such is life,' although rarely is it described in this manner: an inserting itself, a drawing off to its advantage, a parasitizing of the downward course of energy, from its noble solar form to the degraded one of low-temperature heat. In this downward course, which leads to equilibrium and thus death, life draws a bend and nests in it.

Poore soule, in this thy flesh what do'st thou know?
Thou know'st thy selfe so little, as thou know'st not.
How thou did'st die, nor how thou wast begot.
Thou neither know'st how thou at first camest in,
Nor how thou took'st the poyson of mans sin.
Nor dost thou, (though thou know'st, that thou art so)
By what way thou art made immortall, know.
Thou art too narrow, wretch, to comprehend
Even thy selfe; yea though thou wouldst but bend
To know thy body. Have not all soules thought
For many ages, that our body'is wrought
Of Ayre, and Fire, and other Elements?
And now they thinke of new ingredients,
And one soule thinkes one, and another way
Another thinkes, and 'tis an even lay.
Knowst thou but how the stone doth enter in
The bladder's Cave, and never breake the skin?
Knowst thou how blood, which to the hart doth flow,
Doth from one ventricle to th'other go?
And for the putrid stuffe, which thou dost spit,
Knowst thou how thy lungs have attracted it?
There are no passages, so that there is
(For aught thou knowst) piercing of substances.
And of those many opinions which men raise
Of Nailes and Haires, dost thou know which to praise?
What hope have we to know our selves, when wee
Know not the least things, which for our use bee?

The other experiment (which I shall hardly, I confess, make again, because it was cruel) was with a dog, which, by means of a pair of bellows, wherewith I filled his lungs, and suffered them to empty again, I was able to preserve alive as long as I could desire, after I had wholly opened the thorax, and cut off all the ribs, and opened the belly. Nay, I kept him alive above an hour after I had cut off the pericardium and the mediastinum, and had handled and turned his lungs and heart and all the other parts of its body, as I pleased. My design was to make some enquiries into the nature of respiration. But though I made some considerable discovery of the necessity of fresh air, and the motion of the lungs for the continuance of the animal life, yet I could not make the least discovery in this of what I longed for, which was, to see, if I could by any means discover a passage of the air of the lungs into either the vessels or the heart; and I shall hardly be induced to make any further trials of this kind, because of the torture of this creature: but certainly the enquiry would be very noble, if we could any way find a way so to stupify the creature, as that it might not be sensible.

The power of the eye could not be extended further in the opened living animal, hence 1 had believed that this body of the blood breaks into the empty space, and is collected again by a gaping vessel and by the structure of the walls. The tortuous and diffused motion of the blood in divers directions, and its union at a determinate place offered a handle to this. But the dried lung of the frog made my belief dubious. This lung had, by chance, preserved the redness of the blood in (what afterwards proved to be) the smallest vessels, where by means of a more perfect lens, no more there met the eye the points forming the skin called Sagrino, but vessels mingled annularly. And, so great is the divarication of these vessels as they go out, here from a vein, there from an artery, that order is no longer preserved, but a network appears made . up of the prolongations of both vessels. This network occupies not only the whole floor, but extends also to the walls, and is attached to the outgoing vessel, as 1 could see with greater difficulty but more abundantly in the oblong lung of a tortoise, which is similarly membranous and transparent. Here it was clear to sense that the blood flows away through the tortuous vessels, that it is not poured into spaces but always works through tubules, and is dispersed by the multiplex winding of the vessels.

We do not doubt to assert, that air does not serve for the motion of the lungs, but rather to communicate something to the blood ... It is very likely that it is the fine nitrous particles, with which the air abounds, that are communicated to the blood through the lungs.