What is Fermentation. Explanation

The advances in calorimetry in the latter half of the nineteenth century left the core of vitalism untouched, however. Man and the rock he stood upon might both be composed of matter but an impassable line was drawn between forms of matter—first, organic versus inorganic and, when that failed, protein versus nonprotein.

In the same way, the total energy available might be the same for life and nonlife, but surely there was an impassable line between the methods whereby such energy was made available.

Thus, outside the body, combustion was accompanied by great heat and light. It proceeded with violence and rapidity. The combustion of foodstuffs within the body, however, produced no light and little heat. The body remained at a gentle 98.6° F. and combustion within it proceeded slowly and under perfect control. In fact, when the chemist tried to duplicate a reaction characteristic of living tissue he was generally forced to use drastic means: great heat, an electric current, strong chemicals. Living tissue required none of this.

Is this not a fundamental difference? Liebig maintained it was not and pointed to fermentation as an example. From prehistoric times, mankind had fermented fruit juices to make wine and steeped grain to make beer. They had used "leaven" or yeast (as it is more often called) to make dough undergo changes that caused it to puff up with bubbles and make soft, tasty bread.

These changes involve organic substances. Sugar or starch is converted to alcohol and this resembles reactions that go on in living tissue. Yet fermentation does not involve strong chemicals or drastic means. It proceeds at room temperature and in a quiet, slow manner. Liebig maintained that fermentation was a purely chemical process that did not involve life. He insisted it was an example of a change that could take place life fashion, yet without life.

To be sure, since Van Leeuwenhoek's time (see page 29), yeast was known to consist of globules. The globules showed no obvious signs of life, but in 1836 and 1837, several biologists, including Schwann (see page 57), had caught them in the act of budding. New globules were being formed and this seemed to be a sure indication of life. Biologists began to speak of yeast cells. This, however, Liebig did not allow. He did not accept the living nature of yeast.

A French chemist, Louis Pasteur (1822-95), took up the cudgels against the redoubted Liebig. In 1856, he was called in for consultation by the leaders of France's wine industry. Wine and beer often went sour as they aged, and millions of francs were lost as a result. Was there not something a chemist could do?

Pasteur turned to the microscope. He found almost at once that when wine and beer aged properly, the liquid contained tiny spherical yeast cells. When wine and beer turned sour, however, the yeast cells present were elongated. Clearly, there were two types of yeast: one which produced alcohol and one which, more slowly, soured the wine. Heating the wine gently would kill the yeast cells and stop the process. If this were done at the right moment, after the alcohol had formed and before the souring had set in, all would be well. And all was!

In the process, Pasteur made two points quite plain. First, the yeast cells were alive, since gentle heat destroyed their ability to bring about fermentation. The cells were still there; they had not been destroyed, only the life within them had. Second, only living yeast cells, not dead ones, could bring about fermentation. The controversy between himself and Liebig ended in a clear victory for Pasteur and vitalism.

Pasteur went on to perform a famous experiment in connection with spontaneous generation, a subject on which the vitalist position had hardened since Spallanzani's time (see page 34). Biblical evidence in favor of spontaneous generation was now discounted and indeed religious leaders welcomed the disproof of spontaneous generation since that would reserve the formation of life to God alone. It was the mechanists of the mid-nineteenth century who, in some cases passionately, supported spontaneous generation.

Spallanzani had shown that if meat broth were sterilized and sealed away from contamination no life forms would develop in it. Those who were at the time in opposition maintained that heat had destroyed a "vital principle" in the air within the sealed chamber. Pasteur therefore devised an experiment in which ordinary unheated air would not be kept away from the meat broth.

In i860, he boiled and sterilized meat broth and left it open to the ordinary atmosphere. The opening, however, was by way of a long, narrow neck, shaped like an S, lying on its side. Although unheated air could thus freely penetrate into the flask, any dust particles present would settle to the bottom of the S and did not enter the flask.

Under such conditions, the meat broth bred no organisms, but if the neck were removed, contamination followed shortly. It was not a question of heated or unheated air, of a "vital principle" destroyed or undestroyed. It was a matter of dust, some of which consisted of floating microorganisms. If these fell into the broth, they grew and multiplied; if not, not.

The German physician, Rudolf Virchow (see page 69), added to this as a result of his own observations. In the 1850s, he studied diseased tissue intensively (and is therefore considered the founder of the modern science of pathology, the study of diseased tissue) and demonstrated that the cell theory applies to it as well as to normal tissue.

The cells of diseased tissue, he showed, were descended from normal cells of ordinary tissue. There was no sudden break or discontinuity; no eruption of abnormal cells from nowhere. In 1855, Virchow epitomized his notion of the cell theory by a pithy Latin remark which can be translated as "All cells arise from cells."

He and Pasteur together had thus made it quite clear that every cell, whether it was an independent organism or part of a multicellular organism, implied a pre-existing cell. Never had life seemed so permanently and irretrievably walled off from nonlife. Never had vitalism seemed so strong.