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at was very much bigger than a molecule； or gas droplet。
The next step was equally simple to determine whether dead animals were potentially infectious。
He took one of the dead rats and pumped the air out of its cage。 He waited until the air was fully evacuated。 In the pressure fall； the rat ruptured； bursting open。 Burton ignored this。
When he was sure all air was removed； he replaced the air with fresh； clean； filtered air。 Then he connected the cage to the cage of a living animal。
Nothing happened。
Interesting； he thought。 Using a remotely controlled scalpel； he sliced open the dead animal further； to make sure any organisms contained inside the carcass would be released into the atmosphere。
Nothing happened。 The live rat scampered about its cage happily。
The results were quite clear： dead animals were not infectious。 That was why； he thought； the buzzards could chew at the Piedmont victims and not die。 Corpses could not transmit the disease； only the bugs themselves； carried in the air； could do so。
Bugs in the air were deadly。
Bugs in the corpse were harmless。
In a sense； this was predictable。 It had to do with theories of acmodation and mutual adaptation between bacteria and man。 Burton had long been interested in this problem； and had lectured on it at the Baylor Medical School。
Most people； when they thought of bacteria； thought of diseases。 Yet the fact was that only 3 percent of them produced human disease； the rest were either harmless or beneficial。 In the human gut； for instance； there were a variety of bacteria that were helpful to the digestive process。 Man needed them； and relied upon them。
In fact； man lived in a sea of bacteria。 They were everywhere on his skin； in his ears and mouth； down his lungs； in his stomach。 Everything he owned； anything he touched； every breath he breathed； was drenched in bacteria。 Bacteria were ubiquitous。 Most of the time you weren't aware of it。
And there was a reason。 Both man and bacteria had gotten used to each other； had developed a kind of mutual immunity。 Each adapted to the other。
And this； in turn； for a very good reason。 It was a principle of biology that evolution was directed toward increased reproductive potential。 A man easily killed by bacteria was poorly adapted； he didn't live long enough to reproduce。
A bacteria that killed its host was also poorly adapted。 Because any parasite that kills its host is a failure。 It must die when the host dies。 The successful parasites were those that could live off the host without killing him。
And the most successful hosts were those that could tolerate the parasite； or even turn it to advantage； to make it work for the host。
〃The best adapted bacteria；〃 Burton used to say； 〃are the ones that cause minor diseases； or none at all。 You may carry the same single cell of Strep。 viridians on your body for sixty or seventy years。 During that time； you are growing and reproducing happily； so is the Strep。 You can carry Staph。 aureus around； and pay only the price of some acne and pimples。 You can carry tuberculosis for many decades； you can carry syphilis for a lifetime。 These last are not minor diseases； but they are much less severe than they once were； because both man and organism have adapted。〃
It was known； for instance； that syphilis had been a virulent disease four hundred years before； producing huge festering sores all over the body； often killing in weeks。 But over the centuries； man and the spirochete had learned to tolerate each other。
Such considerations were not so abstract and academic as they seemed at first。 In the early planning of Wildfire； Stone had observed that 40 per cent of all human disease was caused by microorganisms。 Burton had countered by noting that only 3 per cent of all microorganisms caused disease。 Obviously； while much human misery was attributable to bacteria； the chances of any particular bacteria being dangerous to man were very small。 This was because the process of adaptation of fitting man to bacteria was plex。
〃Most bacteria；〃 Burton observed； 〃simply can't live within a man long enough to harm him。 Conditions are； one way or another； unfavorable。 The body is too hot or too cold； too acid or too alkaline； there is too much oxygen or not enough。 Man's body is as hostile as Antarctica to most bacteria。〃
This meant that the chances of an organism from outer space being suited to harm man were very slim。 Everyone recognized this； but felt that Wildfire had to be constructed in any event。 Burton certainly agreed； but felt in an odd way that his prophecy had e true。
Clearly； the bug they had found could kill men。 But it was not really adapted to men； because it killed and died within the organism。 It could not be transmitted from corpse to corpse。 It existed for a second or two in its host； and then died with it。
Satisfying intellectually； he thought。
But practically speaking they still had to isolate it； understand it； and find a cure。
***
Burton already knew something about transmission； and something about the mechanism of death： clotting of the blood。 The question remained How did the organisms get into the body？
Because transmission appeared to be airborne； contact with skin and lungs seemed likely。 Possibly the organisms burrowed right through the skin surface。 Or they might be inhaled。 Or both。
How to determine it？
He considered putting protective suitings around an experimental animal to cover all but the mouth。 That was possible； but it would take a long time。 He sat and worried about the problem for an hour。
Then he hit upon a more likely approach。
He knew that the organism killed by clotting blood。 Very likely it would initiate clotting at the point of entrance into the body。 If skin； clotting would start near the surface。 If lungs； it would begin in the chest； radiating outward。
This was something he could test。 By using radioactively tagged blood proteins； and then following his animals with scintillometer scans； he could determine where in the body the blood first clotted。
He prepared a suitable animal； choosing a rhesus monkey because its anatomy was more human than a rat's。 He infused the radioactive tagging substance； a magnesium isotope； into the monkey and calibrated the scanner。 After allowing equilibration； he tied the monkey down and positioned the scanner overhead。
He was now ready to begin。
The scanner would print out its results on a series of human block outlines。 He set the puter printing program and then exposed the rhesus to air containing the lethal microorganism。
Immediately； the printout began to clatter out from the puter：
＇graphic of disease spread in human body＇
It was all over in three seconds。 The graphic printout told him what he needed to know； that clotting began in the lungs and spread outward through the rest of the body。
But there was an additional piece of information gained。 Burton later said； 〃I had been concerned that perhaps death and clotting did not coincide or at least did not coincide exactly。 It seemed impossible to me that death could occur in three seconds； but it seemed even more unlikely that the total blood volume of the body…five quarts…could solidify in so short a period。 I was curious to know whether a single crucial clot might form； in the brain； perhaps； and the rest of the body clot at a slower pace。〃
Burton was thinking of the brain even at this early stage of his investigation。 In retrospect； it is frustrating that he did not follow this line of inquiry to its logical conclusion。 He was prevented from doing this by the evidence of the scans； which told him that clotting began in the lungs and progressed up the carotid arteries to the brain one or two seconds later。
So Burton lost immediate interest in the brain。 And his mistake was pounded by his next experiment。
***
It was a simple test； not part of the regular Wildfire Protocol。 Burton knew that death coinci