12 



PSYCHE. 



[Januarj' — February 1888. 



Pierls rapae and of Datatta ministra^ 

 repeatedly isolating the bacterial species 

 in pure cultures, fluid and solid, on gela- 

 tine films, and in tubes of agar-agar, 

 drawing, photographing, and mounting 

 many slides to illustrate every step of 

 each experiment and finally testing our 

 results, in every case, by applying the 

 supposed disease germs to the food of 

 healthy insects kept in strict comparison 

 with check lots not so treated. By these 

 methods we have clearly discriminated 

 the species of micrococci characteristic 

 of these diseases, as they have occurred 

 with us, and have shown that the spon- 

 taw&ou^Jlachcrie of some of our common 

 caterpillars may be unquestionably con- 

 veyed to other lepidopterous species and 

 even to the white grubs. 



All the bacterial diseases of insects 

 thus far carefully studied, take first and 

 principal effect on tlie epithelial layer 

 of the alimentary canal, — no distinctive- 

 ly blood disease having yet been dis- 

 tinguished, if we except a supposed 

 '■'■Jlacherie^' of Cleomis larvae reported 

 by Metschnikoft' in Russia, but appar- 

 ently not critically investigated. These 

 alimentary schizomycoses are extremely 

 common affections, attacking native in- 

 sects in the open air under all ordinary 

 conditions, and are especially liable to 

 appear among larvae in confinement. 

 I have seen wide-spead epidemics of 

 ■flacherie in the caterpillars of Pieris 

 rapae, of Pyrameis cardui, and of 

 Nephelodes violans, and have met it 

 here and there in numbers of other 

 larvae, both lepidopterous and hymen- 

 opterous. 



For purposes of practical experiment 

 these bacterial diseases have the great 

 disadvantage that they require for the 

 cultivation of their germs, a considerable 



degree of experimental skill and scientif- 

 ic training. They consequently promise 

 less immediate and satisfactory results 

 than the niuscardines. 



In conclusion, gentlemen, I think 

 that you will see why, in trying to 

 present this subject to you, I have not 

 followed a common custom by limiting 

 myself to a summarj^ of the results of 

 the most recent researches ; — it was be- 

 cause so little is generally known to 

 our entomologists on this topic, tliat 

 almost nothing entomological has been 

 done. You can hardly have failed to 

 notice that most of what we know, has 

 been acquired by the economists, like 

 Pasteur, or the botanists, like De Bary 

 and Tulasne — either by those generally 

 indifferent to all but the practical end 

 in view, or else b}^ those using the in- 

 sect organism only as a culture appara- 

 tus for the study of the life histories of 

 fungi. But surely the entomological 

 side of the relation is equally interesting 

 and important — with its unsolved ques- 

 tions of physiology and patholog}', its 

 bearings on distribution as influenced 

 by meteorological conditions, its prom- 

 ised contributions to a knowledge of 

 the details of the struggle for existence, 

 and of the general system of interactions 

 obtaining among organic beings. 



In the strict specialization of modern 

 scientific w^ork, are we not likely to 

 drop many important subjects as be- 

 tween two stools.'' May we not safely 

 recognize a group of specialties which 

 shall comprise the study of the biolog- 

 ical relations of living things, and give 

 to results gathered from this field as 

 cordial and intelligent a reception as to 

 those of the embryologist or the com- 

 parative anatomist.-* 



