154 LOUIS PASTEUR. 



will not show microscopic organisms of any kind, 

 but only cells of parenchyma, green granules of the 

 chloroph} r l of the leaf, and remains of the air-vessels 

 of the plant. Through the action of the liquids 

 secreted by the glands which line the integuments of 

 the intestinal canal, the germs of organisms are them- 

 selves digested or hindered in their development. The 

 digestive functions of silkworms are so active that 

 everything is carried away, destroyed in the same 

 manner as the leaves themselves. 



But if from any cause the digestion of the worms 

 be impeded or suspended, then the germs introduced 

 with the food into the intestinal canal will give rise 

 to the multiplication of microscopic organisms which 

 are always found in the artificially bruised leaf when 

 mixed with a little water. How numerous are the 

 causes which may check this digestive function of the 

 worm a function of such importance to a creature 

 which in the space of one month passes from the 

 weight of half a milligramme to that of five, six, seven, 

 or even eight grammes ! Pastern* proved that when- 

 ever a worm was attacked vtithflacherie, it always had, 

 associated with the food in its intestinal canal, one or 

 other of the microscopic organisms which are in- 

 variably to be met with among crushed mulberry leaves. 

 Summing up in a kind of aphorism a series of ob- 

 servations, Pasteur observes : ' Every rer flat is one 

 which digests badly, and, conversely, every worm 



