480 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



only explanation for this phenomenon at present is, that the cater- 

 pillars we thought healthy and used for the inoculation experiments 

 were really infected with the virus and by giving them great quantities 

 of this bacterium, we simply lowered their resistance to the disease 

 and hastened death, which, in all probabihty, would have occurred 

 sooner or later anyway. Another matter not to be overlooked is the 

 apparent great resistance of many caterpillars towards the virus, 

 provided other invaders or unfavorable conditions are excluded. The 

 caterpillars used in the control experiments in 1912 did not die although 

 doubtless some of them were infected, and the only feasible explana- 

 tion for this seems to be that in one case, i. e., in the inoculation ex- 

 periments, the introduction of great quantities of a specific bacterium 

 lowered the resistance of the animals towards the virus and death 

 followed while in the other case, i. e., in the controls no such bac- 

 terium was introduced. 



Observations made on the blood of a great many individuals fol- 

 lowed by a study of their tissues in section have clearly demonstrated 

 that the polyhedral test for diagnosing the health of caterpillars is by 

 no means absolutely reliable. The blood corpuscles of a caterpillar 

 may not reveal polyhedral bodies, but this does not necessarily mean 

 that the caterpillar is healthy, for sections through such an individual 

 are very likely to show polyhedral bodies in the nuclei of the tissue 

 cells. On the other hand polyhedral bodies may be present in the 

 blood corpuscles and not in the tissues. These observations showed 

 the futility of the blood test in diagnosing. It is a pity that it cannot 

 be used for we have been compelled to substitute a rather more indefi- 

 nite for a presumably more definite method. 



Why Gyrococcus Was Eliminated 



The reasons why we abandoned Gyrococcus flaccidifex are the fol- 

 lowing: If smears are made from caterpillars dead but a short time 

 no bacteria can be found as a rule. Cultures made from such cater- 

 pillars on caterpillar and the ordinary nutrient media remained sterile, 

 except in a very few cases when the bacterium in question again ap- 

 peared. Of course, after a caterpillar has been dead for a certain 

 length of time bacterial invaders entered the body, but cultures made 

 from dying or freshly dead caterpillars rarely manifested growth. 

 At the beginning when the disease first became epidemic in nature 

 we made smears and cultures out in the field by taking with us all 

 the necessary sterilization appliances and in so doing on quiet windless 

 days we found the chances for contamination were very slight as com- 

 pared with those in our laboratory where thousands of caterpillars 

 had previously died. 



