PASTEUR 7 



Dusch. In 1876 Bastian published a communication controverting an early 

 statement by Pasteur that urine, sterilized by boiling, remained free from growth 

 on subsequent incubation. Bastian declared that, if the urine were made alkaline 

 at the start, growth often ensued. Pasteur, on repeating the experiment, was 

 forced to admit the truth of Bastian's statement. A careful retracing of all his 

 steps resulted in the demonstration that fluids with an acid reaction, after steriliza- 

 tion at 100° C, might remain apparently sterile because certain organisms, which 

 remained alive, were unable to develop, while in an alkaline medium they might 

 grow freely. It was found also that ordinary water frequently contained organisms 

 which were not killed by heating to 100° C, and that organisms which had become 

 deposited on the surface of glass-ware in the dry state might withstand far higher 

 temperatures. We know now that it is especially for those bacteria which form 

 spores that these conditions hold true. As a result of this controversy Pasteur 

 established the practice of heating fluid material to 120° C. under pressure for 

 the purpose of sterilization, thus introducing the autoclave into the laboratory, 

 and the practice of sterilizing glass-ware by dry heat at 170° C. In this con- 

 nection a very important advance was made by Tyndall who, observing that 

 actively growing bacteria are easily destroyed by boiling, and that a certain amount 

 of time is required for bacteria in the resistant, inactive phase to pass into the 

 growing phase in which they are heat-sensitive, introduced the method of steriliza- 

 tion by repeated heatings, with appropriate intervals between them. This method 

 is still known as Tyndallization. It was first described in a letter to Huxley in 

 1877 (see Bulloch 1930). 



While investigating the phenomenon of fermentation, and the problem of 

 spontaneous generation, Pasteur had studied the behaviour of very various kinds 

 of natural organic fluids and solutions, and had succeeded in growing micro- 

 organisms on simple synthetic media. As a result he had become assured of the 

 fact that a medium, which is eminently suitable for the growth of one bacterium 

 or mould, may be ill-adapted for the growth of another, and that one of the primary 

 necessities for the successful cultivation of any species of micro-organism is the 

 discovery of a suitable medium for its growth. Quick to grasp the general signi- 

 ficance of isolated observations, he pointed out the decisive effect which must 

 be exercised by the selective action of various environmental factors in determining 

 the constitution of any naturally occurring bacterial flora ; and he later developed 

 these ideas in connection with the problem of infection. 



As the result of these studies Pasteur had collected a mass of data, which 

 enabled him to deal successfully with bacteriological problems that could not 

 previously have been attacked. He had learned the need for the scrupulous 

 sterilization of everything that came into contact with material which was to be 

 submitted to bacteriological examination. He had learned the necessary methods 

 of sterilization, in the steamer, in the autoclave, in the hot-air oven, or by direct 

 flaming, which enabled these conditions to be fulfilled. He had proved the service- 

 ableness of the cotton-wool plug for protecting media in flasks or tubes. He had 

 realized the importance of the constitution of the nutrient material ofiered to a 

 given bacterium, of the acidity or alkalinity of that medium, and of the oxygen 

 pressure to which it was subjected. Armed with this knowledge, he proceeded 

 to break new ground. 



Pasteur was before all else a scientist, intensely curious, and loving knowledge 

 for its own sake, but he was also a convinced utilitarian, and a Frenchman. He 



