New 



Low Price 



$195! 



Haven t you always wanted a weather station? The 

 Weather Wizard ID combines all the most requested 

 features into one incredible package! 

 FEATURES INCLUDE: 



• Inside & • Wind Chill • Instant Metric 

 Outside Temps . Alarms Conversions 



• Wind Speed . Highs & Lows * Optional PC 

 & Direction d ■ - ii ^ .• Interface 



• Rainiall Option 



• Time & Date 



flB Larger Display fflfe Compass Rose 



Order today; 



1-800-678-3669 



M-F 7 a.m. to 5:30 p.m. Pacific Time • NH(342Z 



FAX 1-510-670-0589 • M/C and VISA 

 One-year warranty • 30-day money-back guarantee 



Davis Instruments 



3465 Diablo Ave., Hayward, CA 94545 



Introducing the Revolutionary 



DR* POWER 

 WAGON 



•HAULS UP TO 800 LBS. 



with never-bef ore-ease! • BIG 

 POWER-DRIVEN WHEELS 

 & 4 speed transaxle let you 

 move from a slow walk to 

 a brisk trot over rough or 

 smooth terrain. Power 

 Reverse gets you 

 out of tight 

 spots! 



fREB 



• Dump 

 bed makes for 

 easy unloading of gravel, 

 soil, firewood and rocks. • Made to order for 

 suburban/rural property owners, plus busi- 

 nesses of any size; pays for itself over and 

 over in time and labor saved! 



01994 CHP, Inc. 



Please mail this coupon today for FREE DETAILS 

 including prices, models, and specifications of 

 the Revolutionary DR® POWERWAGON™. 



Name 



Address 



City_ 



State 



_ZIP_ 



To: COUNTRY HOME PRODUCTS®, 20406N 

 L Ferry Road^Box89^Charlotte, VT_ 05445_ 



Vauxhall Company should have suifered 

 from cholera more than residents served 

 by the Lambeth Company. They did. 

 Snow found that the risk of cholera among 

 Southwark and Vauxhall customers was 

 nearly ten times greater in 1853, even 

 though it had not been greater in 1849, 

 when both companies delivered contami- 

 nated water. By showing that cholera 

 could be waterbome, John Snow had es- 

 tablished the field of epidemiology. 



From an evolutionary perspective, the 

 transfer of the "foul linen," the movement 

 of contaminated sewage into water sup- 

 plies, and the delivery of contaminated 

 drinking water acted like a horde of mos- 

 quitoes transmitting pathogens from im- 

 mobilized patients. Might such water- 

 bome transmission be responsible for the 

 great variability in harmfulness found 

 among diarrheal pathogens? A quick look 

 at the literature cannot resolve this ques- 

 tion because most diarrheal organisms can 

 sometimes be transmitted by water and 

 sometimes not. My task, therefore, was to 

 determine from the literature whether se- 

 vere organisms tended to be waterbome 

 more often than were milder organisms. 



By the time I looked out of the train 

 window, I was a few years into this task. A 

 pattem was taking shape: the lethality of 



London 's Lambeth Company opened a 

 new waterworks in 1852. Its customers 

 therefore received relatively pure water 

 and largely escaped a cholera epidemic 

 that ravaged the city the following year. 



The Granger Collection 



the various diarrheal bacteria correlated 

 almost perfectly with their tendencies to 

 be waterbome. The correlation explained 

 why cholera, typhoid fever, and some 

 kinds of dysentery were so severe. It also 

 suggested a new dimension for disease 

 control. If waterbome transmission favors 

 the evolution of increased harmfulness, 

 then water purification should do the op- 

 posite — transform severe pathogens into 

 milder ones. Indeed, records indicate that 

 this transition has happened. Pohcy mak- 

 ers, however, have recently diverted in- 

 vestments from clean-water programs be- 

 cause field studies did not show a large 

 reduction in frequencies of infection. But 

 frequencies are only part of the story, the 

 epidemiological part, the part that Snow 

 was investigating. The severity per infec- 

 tion is the other important part, the evolu- 

 tionary part. If the next generation of pre- 

 cise tests shows that water purification 

 transforms severe organisms into mild 

 ones, then we will have a powerful evolu- 

 tionary tool for taming diarrheal disease. 



These ideas forge a link between epi- 

 demiology and evolutionary biology, be- 

 tween John Snow and Charles Darwin. Al- 

 though Snow and Darwin were long dead, 

 I felt as though I had been meeting with 

 them — their printed words had launched 

 their insights through the intervening cen- 

 tury. When I looked out of the train win- 

 dow I was aloft with these thoughts, but 

 just as I was coming back to earth, I left it 

 again when I saw a sign at the train station: 

 Vauxhall! Until then the places in Snow's 

 book had just been markers for keeping 

 track of disease outbreaks. But at that mo- 

 ment I realized that I was having both an 

 intercentury tutorial from Snow and a tour 



THE LAMBETH WATER C >f I' A N Y * S N E ^V W R I 



44 Natural History 6/94 



