In this biography of Louis Pasteur good use is made of the laboratory notebooks that Pasteur once asked his family to keep forever from public view. It is only recently that these important documents entered the public domain, but they are now available to anyone who has access to the manuscript room of the Biblioth que Nationale in Paris. They came there as part of a vast collection of unpublished papers still in the hands of relatives; and Gerald Geison promptly set himself the task of deciphering Pasteur's day-by-day recording of thousands of experiments. He did this knowing that no scientific biography is complete unless it shows how raw data are converted into published results; and realising that, in relation to Pasteur's scientific career, there was now a totally new set of "texts" to read. From the facsimiles selected for publication one can see that the task of notebook deciphering will take decades to complete. Meanwhile, by taking one example from each type of experiment (chemical, animal and human) Geison has shown "that the standard Pastorean legend needs to be qualified, even transformed".

According to this legend Pasteur was "the great and selfless benefactor of humanity who single-handedly slashed through the prejudices of his time to discover a set of scientific principles unmatched in their impact on the daily lives and well-being of humankind". Insofar as the Pasteur Institute in Paris is literally a shrine as well as a centre of biomedical research, this legend is set in stone. But from Geison's archival research has come evidence that, although Pasteur was a brilliant experimentalist, he was no exemplar of modesty or ethical rectitude. On the contrary, he often failed to give credit where credit was due, and was not above deliberately deceiving his scientific peers.

Pasteur's first claim to fame was the result of solving a problem of great importance to chemical theory. He did this by showing that although one of two soluble salts with exactly the same chemical reactions and molecular components consisted of a single set of hemihedral crystals, the other could be separated into two sets - identical in every respect except that the crystals were mirror images of one another. The notebooks show that this discovery was the result of work by Auguste Laurent - which showed that when substances have the same crystalline form they necessarily have the same type of optical activity - and work by Pasteur who was desperately trying to find the reason for an apparent exception to the Laurentian rule. But the world has been led to believe that Pasteur, with exceptional brilliance, suddenly realised that, when one of two otherwise identical substances deflects polarised light to the right and the other is optically inactive (the only known difference between the two salts he was studying) the inactive one must consist of equal parts of dextro- and laevo-rotary crystals. Even in his famous lecture of 1860 there was no mention by Pasteur either of the true sequence of events or his debt to a close colleague and mentor.

Pasteur spent several years establishing correlations between optical activity and crystalline form. But he also had an opportunity to study the etiology of silkworm blight and soon began paying close attention to the life-like and death-related processes of fermentation and putrefaction. He was now on the path which was to lead (via ingenious tests of the current doctrine of spontaneous generation) to two famous achievements: putting the germ theory of disease firmly on the scientific map, and producing vaccines against various diseases.

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By deliberate avoidance of any focused attention on the studies of silkworm diseases, we are led by Geison straight from Pasteur's speculations about "asymmetric forces and the origin of life" to "The Secret of Pouilly-le-Fort: Competition and Deception in the Race for the Anthrax Vaccine". This secret refers to a public and highly successful test of Pasteur's method of rendering sheep immune to anthrax. Everyone assumed they were witnessing the effects of an oxygen attenuated vaccine and, without actually saying so, Pasteur did everything to encourage this idea. However, the notebooks show that he actually (and deliberately) used a chemically attenuated vaccine. Why he took this unusual step is not clear, since his usual (oxygen attenuation) method soon met with general approval. But the deception was clearly the result of a rival scientist, Henri Toussaint, having an earlier, albeit temporary success with a different type of chemical attenuation.

A third series of experiments to show discrepancies between the public and private science of Pasteur includes his first "private patient" and the animal experiments that were supposed to justify the giving of a live rabies vaccine to anyone recently bitten by a rabid dog. According to the public record, Pasteur only agreed to treat Joseph Meister after rendering 50 normal dogs immune to rabies "without a single failure", and after having similar successes with "large numbers" of dogs in the same predicament as Meister. But according to the notebooks, by the time the boy was given his first injection only ten unbitten dogs had received the first of several injections more than 30 days before, and none of the bitten dogs received the same treatment as the bitten youth.

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The successful treatment of Meister received high acclaim and heralded the final phase of Pasteur's career. He was now a national hero and so world famous that what he netted in special awards and fees was sufficient to build and run the Pasteur Institute. Nevertheless, the only medically qualified person to know the true state of play (Emile Roux) refused to have anything to do with the Meister episode and only later decided that the ends had justified the means. We are now approaching the end of the only biography to catch even a glimpse of Pasteur's "private science". All that remains is a final chapter which deals with various aspects of the Pastorean myth and leaves us with what is clearly a true portrait, warts and all.

Alice Stewart is senior research fellow, department of epidemi-ology, University of Birmingham.