微生物学 1861

论大气中存在的有组织微粒——对自然发生学说的检验

路易·巴斯德

他在一只弯颈烧瓶里把肉汤煮沸——并证明：瓶中出现的生命是随尘埃飘进来的，绝非凭空而生。

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In depth · the introduction

两千年来，人们相信生命能径直从肉汤与腐物中冒出。一段弯曲的玻璃瓶颈，证明他们错了。

核心想法

把肉汤搁在外面，几天之内便会爬满微小的生命。几个世纪里，最顺理成章的解释是：肉汤本身孕育了这些生物——生命从无生命中诞生，即「自然发生」。路易·巴斯德却认为真相更简单、也更奇异：空气里满是看不见的活微生物，乘着尘埃飘游，它们只不过是落了下来、繁殖开来罢了。

要证明这一点，他得让空气接触肉汤、却把尘埃挡在外面——因为批评者坚称，密封烧瓶会「败坏」空气，于是任何无菌的结果都算作弊。他的答案，是一只瓶颈被向下弯成 S 形的烧瓶：鹅颈瓶。

它是如何诞生的

巴斯德是化学家，而非生物学家，他是侧着身子走进微生物世界的——经由发酵，他证明把葡萄汁变成酒、把牛奶变酸的，是酵母与细菌这些活物，而非单纯的化学。这让他确信空气携带着生命，也把他卷入了那个时代最激烈的生物学争论。他的主要对手、博物学家费利克斯·普歇是位严肃的科学家，自有一套似乎显示「生命凭空出现」的实验。

巴斯德的鹅颈瓶是决定性的一击：煮沸、敞开，却始终澄澈——直到他把一只瓶子倾斜，让肉汤淌进积着尘埃的弯颈，数日之内它便浑浊起来。他还把烧瓶带上阿尔卑斯山，证明更洁净、更高处的空气，播下的染菌要少得多。1862 年，法国科学院为这项工作授予他奖项；就寻常意义而言，此案就此了结。

它为何重要

如果微生物乘空气而来、并由同类繁衍，那它们就能被挡在外面——单单这一个想法，便重组了医学与食品。外科医生学会了不让微生物进入伤口（李斯特的抗菌术）；医院学会了灭菌；我们学会了把食物装罐，把牛奶与葡萄酒「巴氏消毒」——温和加热以杀灭微生物，而这个词，正是巴斯德的名字。而最重要的是，疾病本身从此可以被理解为特定活体生物所致的感染——现代微生物学与大半医学，皆奠基于此。

一个可以想象的画面

想想厨房水槽下那段 U 形弯管。它里头总存着一点水，正是这个「存水弯」拦住了下水道的臭味与污浊，不让它们返回屋里——而空气仍可通过。巴斯德的鹅颈是同一巧思的反用：弯处是个陷阱，截住从进来的空气里沉降的尘埃与微生物，使它们永远到不了肉汤。把液体倾进这个陷阱，你就等于把截下的微生物，径直冲回了自己那份干净的肉汤里。

它的位置

巴斯德站在一场漫长争论的终点：弗朗切斯科·雷迪早在 1668 年就让盖好的肉里不再生蛆，拉扎罗·斯帕兰扎尼又在 1765 年煮沸并封存了烧瓶，可两人都堵不住关于「空气」的反驳。巴斯德把它堵上了。他的结果，与本馆其他文献直接相通——约翰·斯诺方才论证霍乱经水而传（1855），约瑟夫·李斯特将把细菌学说带进外科（1867），而亚历山大·弗莱明的青霉素（1929），日后将对巴斯德最早在空气中捕获的那些微生物，反将一军。

The original document

Original source text

Louis Pasteur · Mémoire sur les corpuscules organisés qui existent dans l'atmosphère · Annales des sciences naturelles, 4e série, t. 16 · Paris, 1861

Pasteur's thesis: the living things that appear in a boiled, decaying infusion are not generated by the broth itself. They grow from germs — minute organisms suspended in ordinary air, riding on its dust. Keep the dust out, and however freely the air comes and goes, nothing will ever live in the liquid.

The doctrine on trial

For two millennia it was taken for granted that life arises spontaneously from non-living matter — maggots from meat, mice from grain, swarms of microscopic 'animalcules' from any broth left to stand. Redi (1668) had banished the maggots, and Spallanzani (1765) had shown that a sealed, boiled flask stays lifeless; but his critics had a ready answer. Sealing and prolonged boiling, they said, spoils the air or destroys some 'vital force' it carries, so the absence of life proves nothing. To settle it, an experiment was needed that admitted fresh air in full — and excluded only the dust.

The swan-neck flask

Pasteur drew the neck of a flask out in a flame into a long, downward S — a 'swan neck' (col de cygne). He boiled the broth to sterilise it and left the flask open to the air. Air passed freely in and out; but the dust it carried, and the germs upon it, settled in the low bend of the neck and never reached the liquid. The broth stayed clear for months, for years. Then, tilting the flask so the broth ran up into the bend and back, he washed the trapped dust into the liquid — and within days it teemed with life. The air had never been the issue. The dust was.

There is no known circumstance in which it can be affirmed that microscopic beings came into the world without germs, without parents similar to themselves.

[ … ]

Before the Academy

Pasteur reinforced the case from every side. Drawing air through a plug of gun-cotton, he dissolved the plug and found under the microscope a litter of 'organized corpuscles' indistinguishable from the germs that grew in his flasks. Exposing sterile flasks at different places, he found that ordinary cellar and street air seeded almost all of them, while air from a high Alpine glacier seeded very few — the germs were unevenly scattered through the atmosphere, not everywhere and inevitable. For this body of work the Académie des sciences awarded him its prize on spontaneous generation in 1862.

From the 1864 Sorbonne address

Louis Pasteur · « Des générations spontanées », a public lecture · Sorbonne, Paris · 7 April 1864

Never will the doctrine of spontaneous generation recover from the mortal blow that this simple experiment deals it.

Paris · École Normale Supérieure · 1861