Bacterial Disease of the Squash-ljug. 363 



for it seemed impossible that an effect so markod could 

 result from any circumstances concomitant to the mere 

 presence of the bacteria in the water. Nevertheless, 

 similar experiments were made with other active aerobic 

 bacteria; but in these infusions no such marked or per- 

 manent effects could be induced. 



In general, soft-skinned insects were much more readily 

 affected; and the yellow-necked apple-tree caterpillar, 

 Jjdtana wdnistra, proved to be an excellent subject for 

 experimentation. I give in detail a record of the effect 

 on one of these larvae, as made by Professor Forbes: 

 The larva was dipped for ten seconds in a strong in- 

 fusion of the bacteria, and then removed to a piece of 

 filter paper for observation. On removal it was quite 

 rigid, but in two minutes there were slight signs of life, 

 and in three minutes it was wriggling and tossing, con- 

 tinuing these incoherent movements until after the fifth 

 minute, when it lay quietly upon its back. Six minutes 

 after removal from the infusion, the larva ceased en- 

 tirely to respond to touch, and was apparently dead. 

 It was kept for twenty-four hours more, but gave no 

 evidence of recovery. Such insects as squash-bugs, flies, 

 etc., often make characteristic movements when about 

 to succumb to this poison; and in the stiffness that 

 finally ensues, the legs are often closely drawn together. 

 As mentioned before, many insects will recover from the 

 effect if removed as soon as they become stiff. I shall 

 have further occasion to refer to this stiffness produced 

 in insects previous to death, and as it is doubtless 

 analagous to certain effects of heat, cold, etc., we may 

 conveniently employ for it the term toxic rigor. 



In order to avoid any possibility of confounding with 

 these toxic phenomena those incident to drowning, a 

 number of water-beetles {Dineutes discolor) were secured 

 for experimentation. It was first ascertained that a 

 water-beetle easily lives in pure bouillon many hours- 

 thirty in the case recorded; and after such a length of 



