298 READINGS IN BIOLOGICAL SCIENCE 



more and it is on them and the always-troublesome mental diseases that 

 science has now turned the bulk of its attention. 



ENTER LOUIS PASTEUR * 

 E. C. LARGE 



In 1 86 1, Albert, Prince Consort of England, died of typhoid fever. There 

 was then no knowledge of the real nature or cause of typhoid fever, and, 

 a fortiori, no knowledge of the hygienic or prophylactic measures by 

 which his regrettably early decease from this cause might have been pre- 

 vented. If anyone had suggested that the good Prince died because of the 

 multiplication in his intestinal tract of a microscopic fission-fungus, nour- 

 ished by the royal juices and brewing virulent poisons in them, that person 

 would have been considered mad. A very great deal more was known about 

 the Potato Blight by 1861 than about typhoid fever. The fungal organism 

 that caused the Potato Blight was known, at least in part; the bacillus of 

 typhoid was not even identified until 1884. 



That typhoid was an infectious disease was apparent to everybody; in 

 epidemics it spread among men almost as fast as the Blight spread in the 

 potato fields, but the agency by which it was communicated from one 

 person to another was a mystery. There might be pernicious "miasmas" 

 or the Disease itself might have "germs" — much as one might speak of the 

 germs of an idea. The "germs" might even have a material existence, for all 

 kinds of notions of germs had been the playthings of the philosophers for 

 about as long as there had been any philosophers in the world. But in 1861 

 the notions about germs were even more nebulous than those about "atoms" 

 before Dalton. Nobody seriously imagined that the germs of typhoid fever 

 would ever be seen, measured, counted, and cultivated in dishes and test- 

 tubes. 



One very good reason why knowledge of the bacteria — a few species 

 of which were subsequently found to cause infectious diseases of man — 

 lagged so far behind that of the micro-organisms associated with the prin- 

 cipal diseases of plants was that the bacteria were of a second order of 

 smallness, and of deceptively-insignificant appearance when seen with even 

 the highest powers of the microscopes available. The spore-bearing hyphae 

 of the Potato Blight fungus, the summer and winter fruits of the common 

 Powdery Mildew of the Rose, the germinating spores of the Bunt fungus 

 of the wheat — they all appeared comparatively large when magnified some 

 three hundred and fifty diameters, and they were easy to recognize as 

 organized vegetable growths. But even yeast cells appeared very small at 

 that magnification, and the several forms of bacteria were smaller still, 



* From The Advafice of the Fungi by E. C. Large, Henry Holt and Company, New 

 York. 



