Contagious Diseases of Insects. 261 



learn whether it is characterized by bacteria ; and (3) whether 

 it is practically contagious. Determining these questions affirm- 

 atively, (4) cultures of the baqteria must be made artificially, 

 and (5) these cultures must be used to produce, in healthy 

 insects of the same or other species, a disease characterized by 

 the symptoms and results of the original affection. It is fur- 

 ther desirable that (6) second cultures should be prepared 

 from these cases of disease artificially produced, in order that 

 a strict comparison may be made of the bacteria concerned, as 

 they occur both in the bodies of the insects and in artificial cul- 

 ture fluids. 



I propose to take up these points seriatim, (first with 

 respect to ftacherie in the cabbage worm), presenting separately 

 the facts bearing upon each, only premising that the proof of 

 one proposition is sometimes partly contained in the data relat- 

 ing chiefly to another, so that some repetition will be neces- 

 sitated by this mode of discussion; but this disadvantage will 

 doubtless be found insignificant, compared with the gain in 

 clearness and* cogency. 



Description of Flacherie in the Cabbage Worm. 



In this insect flacherie is distinguishable with great ease 

 and certainty by conspicuous external symptoms, the color 

 alone of affected larvae being, in fact, entirely characteristic and 

 unmistakable. The natural color of a healthy cabbage worm is 

 a light lively green, sometimes slightly tinged with yellowish, 

 but without any approach to an ashy or milky hue. As the 

 first symptom of ftacherie, however, the larva commences to 

 turn pale, this paleness increasing more or less rapidly until the 

 color is almost milky white, only slightly tinged with greenish. 

 This discoloration is uniform and simple, no other tint usually 

 appearing until after death. Then, however, the color deepens 

 to a sooty gray, commonly uniform, but sometimes appearing 

 first about the center of the length of the larva. Occasionally 

 this deeper color appears a little before death, but it is not then 

 of equal depth over the whole surface. 



In the actions of the insect there is little to indicate any 

 change of state^ except a gradually increasing sluggishness, 



