THE SILKWORM-DISEASE. 147 



which falls upon the leaf and fouls it. This is the 

 excreta of the worms, which the microscope shows to 

 be more or less filled with corpuscles drawn from the 

 lining of the intestinal canal. It is there that they 

 swarm. It is easy to understand that these excreta, 

 falling on the leaves, contaminate them all the more 

 easily because the worms, by the weight of their bodies 

 in crawling, press the excreta against the leaves. 

 This is one cause of natural contagion. By the ex- 

 creta of corpusculous worms which he crushed, mixed 

 with water, and spread with a paint-brush over the 

 mulberry leaves intended for a single meal, Pasteur 

 was able to communicate the contagion to as many 

 worms as he liked. 



He also indicated another natural and direct cause 

 of contagion. The six fore-feet of the worm have 

 sharp hooks at their ends, by means of which the 

 worms prick each other's skins. Let any one imagine 

 a healthy worm passing over the body of the corpus- 

 culous worm. The hooks of the first worm, by pene- 

 trating the skin of the second, are liable to be soiled 

 by the corpuscles immediately below that skin ; and 

 these hooks are capable of carrying the seeds of dis- 

 ease to other healthy worms, which may be pricked in 

 their turn. To demonstrate experimentally, as Pas- 

 teur did, the existence of this cause of contagion, it 

 was only necessary to take some worms and allow 

 them to wound each other. Lastly, infection at a 



