140 SCIENCE REMAKING THE WORLD 



food, the mulberry leaves; that the full-grown worms 

 might spin good cocoons from which the workers could 

 unravel the desired silk; that enough good cocoons 

 should be left to produce adult moths to continue pro- 

 duction of new supplies of healthy eggs. 

 1 Pasteur began this study in 1865. He studied the 

 eggs and found within some of them certain small 

 bodies resembling the smallest animal cells. He called 

 these bodies corpuscles, simply meaning "small bodies." 

 He notecf that when eggs which contained the cor- 

 puscles hatched, the worms were sickly and usually 

 died. Using his crude microscope, he separated the 

 eggs which contained no corpuscles and caused them to 

 natch. The worms thus produced seemed to be healthy, 

 and after careful work, Pasteur announced that people 

 'could produce healthy worms and good cocoons by se- 

 lecting eggs which contained no corpuscles. When this 

 was tried and failed, Pasteur patiently returned to his 

 microscopic studies and found another small organism, 

 a bacterium, and immediately concluded that the silk- 

 worms had two diseases instead of one. One, pebrine, 

 was caused by the animal corpuscles; and the other, 

 flacherie, caused by bacteria. Through long and care- 

 ful experiments he discovered that eggs selected so as 

 to be free from corpuscles and bacteria would produce 

 healthy worms; that such worms when grown upon 

 fresh mulberry leaves would mature and produce good 

 silk cocoons; but that even healthy worms when grown 

 were likely to sicken and die. He thus concluded that the 

 corpuscles and bacteria produce the diseases, and that 

 .diseases from sick w T orms may be transmitted to healthy 



