CAUSATION OF DISEASE 23 



flasks with long necks drawn out to a point and bent over. 

 These permitted a full access of air by diffusion but kept 

 out living germs, since these cannot fly but are carried 

 mechanically by air currents or fall of their own weight 

 (Fig. 5). Hoffman, the year before (1860), had made similar 

 experiments but these remained unnoticed. The Pasteur 

 flasks convinced most scientists that "spontaneous genera- 

 tion" has never been observed by man, though some few, 

 notably Dr. Charlton Bastian, of England, vigorously sup- 

 ported the theory from the early seventies until his death 

 in November, 1915. 



John Tyndall, in combating Bastian's views, showed that 

 boiled infusions left open to the air in a closed box through 

 which air circulated did not show any growth of organisms 

 provided the air was so free of particles that the path of a 

 ray of light sent through it from side to side could not be 

 seen (Fig. 6). Or if such sterilized infusions were exposed 

 to dust-free air, as in the high Alps, the majority showed no 

 growth, while all infusions in dusty air did show an abun- 

 dance of organisms. Tyndall's experiments confirmed those 

 of Pasteur and his predecessors and showed that the organ- 

 isms developed from "germs" present in the air falling into 

 the liquids and not spontaneously. 



CAUSATION OF DISEASE. 



Apparently the first writer on this subject was Varo; about 

 B.C. 70, who suggested that fevers in swampy places were 

 due to invisible organisms. Fracastorius (1484^1553), in 

 a work published in 1546, elaborated a theory of "disease 

 germs" and "direct and indirect contagion" very similar to 

 modern views, thougli based on no direct pathological knowl- 

 edge. Nevertheless Kircher (mentioned already) is usuafly 

 given undeserved credit for the "contagium vivum" theory. 

 In 1657 by the use of simple lenses he observed "worms" in 

 ■ decaying substances, in blood and in the pus from bubonic 

 plague patients (probably rouleaux of corpuscles in the 

 blood, certainly not bacteria in any case). Based on these 

 observations and possibly also on reading the work of 



