a history of science-4-第46章
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
working microbiologist。
As it happened； the world was not kept long in suspense。 Almost before the proposition had taken shape in the minds of the other leaders； Pasteur had found a solution。 Guided by the empirical success of Jenner； he； like many others； had long practised inoculation experiments； and on February 9； 1880； he announced to the French Academy of Sciences that he had found a method of so reducing the virulence of a disease germ that when introduced into the system of a susceptible animal it produced only a mild form of the disease； which； however； sufficed to protect against the usual virulent form exactly as vaccinia protects against small…pox。 The particular disease experimented with was that infectious malady of poultry known familiarly as 〃chicken cholera。〃 In October of the same year Pasteur announced the method by which this 〃attenuation of the virus；〃 as he termed it； had been brought aboutby cultivation of the disease germs in artificial media； exposed to the air； and he did not hesitate to assert his belief that the method would prove 〃susceptible of generalization〃that is to say； of application to other diseases than the particular one in question。
Within a few months he made good this prophecy； for in February； 1881； he announced to the Academy that with the aid； as before； of his associates MM。 Chamberland and Roux； he had produced an attenuated virus of the anthrax microbe by the use of which； as he affirmed with great confidence； he could protect sheep； and presumably cattle； against that fatal malady。 〃In some recent publications；〃 said Pasteur； 〃I announced the first case of the attenuation of a virus by experimental methods only。 Formed of a special microbe of an extreme minuteness； this virus may be multiplied by artificial culture outside the animal body。 These cultures； left alone without any possible external contamination； undergo； in the course of time； modifications of their virulency to a greater or less extent。 The oxygen of the atmosphere is said to be the chief cause of these attenuationsthat is； this lessening of the facilities of multiplication of the microbe； for it is evident that the difference of virulence is in some way associated with differences of development in the parasitic economy。
〃There is no need to insist upon the interesting character of these results and the deductions to be made therefrom。 To seek to lessen the virulence by rational means would be to establish； upon an experimental basis； the hope of preparing from an active virus； easily cultivated either in the human or animal body； a vaccine…virus of restrained development capable of preventing the fatal effects of the former。 Therefore； we have applied all our energies to investigate the possible generalizing action of atmospheric oxygen in the attenuation of virus。
〃The anthrax virus； being one that has been most carefully studied； seemed to be the first that should attract our attention。 Every time； however； we encountered a difficulty。 Between the microbe of chicken cholera and the microbe of anthrax there exists an essential difference which does not allow the new experiment to be verified by the old。 The microbes of chicken cholera do not； in effect； seem to resolve themselves； in their culture； into veritable germs。 The latter are merely cells； or articulations always ready to multiply by division； except when the particular conditions in which they become true germs are known。
〃The yeast of beer is a striking example of these cellular productions； being able to multiply themselves indefinitely without the apparition of their original spores。 There exist many mucedines （Mucedinae？） of tubular mushrooms； which in certain conditions of culture produce a chain of more or less spherical cells called Conidae。 The latter； detached from their branches； are able to reproduce themselves in the form of cells； without the appearance； at least with a change in the conditions of culture； of the spores of their respective mucedines。 These vegetable organisms can be compared to plants which are cultivated by slipping； and to produce which it is not necessary to have the fruits or the seeds of the mother plant。
The anthrax bacterium； in its artificial cultivation； behaves very differently。 Its mycelian filaments； if one may so describe them； have been produced scarcely for twenty…four or forty…eight hours when they are seen to transform themselves； those especially which are in free contact with the air； into very refringent corpuscles； capable of gradually isolating themselves into true germs of slight organization。 Moreover； observation shows that these germs； formed so quickly in the culture； do not undergo； after exposure for a time to atmospheric air； any change either in their vitality or their virulence。 I was able to present to the Academy a tube containing some spores of anthrax bacteria produced four years ago； on March 21； 1887。 Each year the germination of these little corpuscles has been tried； and each year the germination has been accomplished with the same facility and the same rapidity as at first。 Each year also the virulence of the new cultures has been tested； and they have not shown any visible falling off。 Therefore； how can we experiment with the action of the air upon the anthrax virus with any expectation of making it less virulent？
〃The crucial difficulty lies perhaps entirely in this rapid reproduction of the bacteria germs which we have just related。 In its form of a filament； and in its multiplication by division； is not this organism at all points comparable with the microbe of the chicken cholera？
〃That a germ； properly so called； that a seed； does not suffer any modification on account of the air is easily conceived； but it is conceivable not less easily that if there should be any change it would occur by preference in the case of a mycelian fragment。 It is thus that a slip which may have been abandoned in the soil in contact with the air does not take long to lose all vitality； while under similar conditions a seed is preserved in readiness to reproduce the plant。 If these views have any foundation； we are led to think that in order to prove the action of the air upon the anthrax bacteria it will be indispensable to submit to this action the mycelian development of the minute organism under conditions where there cannot be the least admixture of corpuscular germs。 Hence the problem of submitting the bacteria to the action of oxygen comes back to the question of presenting entirely the formation of spores。 The question being put in this way； we are beginning to recognize that it is capable of being solved。
〃We can； in fact； prevent the appearance of spores in the artificial cultures of the anthrax parasite by various artifices。 At the lowest temperature at which this parasite can be cultivatedthat is to say； about ＋16 degrees Centigradethe bacterium does not produce germsat any rate； for a very long time。 The shapes of the minute microbe at this lowest limit of its development are irregular； in the form of balls and pearsin a word； they are monstrositiesbut they are without spores。 In the last regard also it is the same at the highest temperatures at which the parasite can be cultivated； temperatures which vary slightly according to the means employed。 In neutral chicken bouillon the bacteria cannot be cultivated above 45 degrees。 Culture； however； is easy and abundant at 42 to 43 degrees； but equally without any formation of spores。 Consequently a culture of mycelian bacteria can be kept entirely free from germs while in contact with the open air at a temperature of from 42 to 43 degrees Centigrade。 Now appear the three remarkable results。 After about one month of waiting the culture diesthat is to say； if put into a fresh bouillon it becomes absolutely sterile。
〃So much for the life and nutrition of this organism。 In respect to its virulence； it is an extraordinary fact that it disappears entirely after eight days' culture at 42 to 43 degrees Centigrade； or； at any rate； the cultures are innocuous for the guinea…pig； the rabbit； and the sheep； the three kinds of animals most apt to contract anthrax。 We are thus able to obtain； not only the attenuation o
