170 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 7 



a chemical reduction of the insect, an action that is vigorous at first 

 but after a few weeks or days gives place to a chemical deposit of 

 sulphur. The effects are thus not altogether immediate, but pro- 

 longed, and the reactions grow weaker day by day. That the San 

 Jose scale is able to resist the first shock of deoxygenation is evident 

 from the abundance of living scales for several weeks after the appli- 

 cation. 



It is a difficult matter to determine just when a scale insect dies. 

 A killed scale becomes dry in a few days, during which time its pro- 

 toplasm changes from a pale yellow juicy condition, through a viscous 

 sirupy stage, to a darker yellow oily meal. This reaction is not 

 reversible, and thus dift'ers from the first effects of dessication, from 

 which insects may be revived. In making counts of the scales we 

 rated as dead all insects that showed gelation of the protoplasm when 

 crushed under the microscope. 



That the San Jose scale should become acclimatized to a sulphur- 

 lime environment is not altogether a strange thing. There are organ- 

 isms living in sulphur springs, in thermal springs, in hypertonic salt 

 and alkaline lakes, and even in petroleum wells, — all of them environ- 

 ments fatal to normal forms. An example of such abnormal species 

 in the making can be readily observed in an estuarial tension life- 

 zone, where the salt water forms are invading the fresh water region, 

 and the fresh water species are becoming adapted to the recurring 

 tides. 



One of the strangest instances of acclimation is the case of arsenic 

 eaters. By consuming repeated small amounts of arsenic the body 

 becomes immune to many times the normal lethal dose. When 

 arsenic spraying for leaf-eating insects is imperfectly done it is quite 

 possible for the insects to get daily homeopathic doses of arsenic 

 and to become progressively resistant. Indeed, Mr. R. W. Glaser of 

 the Bussey Institution, has experimentally verified this supposition 

 in his work with the gipsy moth. By successively administering more 

 and more spray, he tells me that he has succeeded in rearing a series 

 of moths from larva? that finally were feeding on heavy dosages of 

 arsenate of lead. Indeed, these larvse were especially hardy, and 

 developed as strong an immunity to disease as they did to the arsenic. 

 This may be the underlying reason why spraying for half-grown cater- 

 pillars and grasshoppers is usually so ineffective. 



While immunity to arsenic may be a greater factor in the control 

 of insects than we at present know, yet it is an adaptation of the 

 individual only. We do not know that such an acquired immunity 

 affects subsequent generations, although it would not be inconceivable 

 that arsenic antibodies are passed on by the mother into the egg to 

 give the offspring some initial immunity. 



