PSYCHE. 



[January — F'ebruar)' iSS8. 



tive character which have been traced 

 to fungus or protozoan parasites as 

 their causes. 



Within these limits, I will under- 

 take to summarize briefly existing 

 knowledge concerning the leading 

 forms of contagious insect disease, with 

 such references to foreign literature as 

 may be necessary, and with a fuller 

 analysis of our scanty American contri- 

 butions. 



Of the protozoan diseases of insects, 

 pibrlne of the silkworm is the best 

 known example, — an affection which 

 has for the insect world a character so 

 deadly as quite to overshadow any form 

 of animal parasitism known among 

 human kind. It is a plague rapidly 

 and easily conveyed by contamination 

 of the food, and exceedingly liable to 

 hereditary transmission through infec- 

 tion of the forming egg in the ovary, — 

 differing in this latter respect from any 

 other insect affection known to me. 



First clearly distinguished about 

 thirty years ago, it has been thoroughly 

 studied in most of its relations, and is 

 now described, as it occurs in the silk- 

 worm, in every general work on silk 

 culture, a very intelligent summary of 

 its characters being given, for example, 

 in Maillot's Lemons sur le ver h sole du 

 miirier. The best detailed description 

 which 1 have seen of its symptoms and 

 histology is that by Qiiatrefages in his 

 Etudes sur les maladies actuclles du 

 ver hj sole* (p. 229-306), to be read, 



*Memoires de V Academic des scieftces de Vlnstitut 

 imperial de Fraiice, tome 30. 



however, in connection with Pasteur's 

 critical remarks in his Etudes sur les 

 maladies des vers d sole (v. i, p. 99- 

 ro6). 



Its most evident symptoms are, ex- 

 ternally, the peculiar black specking 

 of the skin, from which it derives its 

 name, and, internally, the appearance 

 of similar black spots on the organs 

 generally ; and, in the blood, of the 

 peculiar spores of parasites ("corpus- 

 cles" of Cornalia) to be mentioned 

 later. Its characteristic pathological 

 features are (i) the more or less ex- 

 tensive disorganization of the gastric 

 epithelium, witliin whose cells the 

 parasites begin their development ; 

 and (2) the general invasion of nearly 

 all the internal tissues by tliese para- 

 sites and their spores, which also be- 

 come abundant in the blood. At death 

 the body has a certain elasticity quite 

 in contrast with the flaccid condition of 

 larvae dead with other forms of con- 

 tagious disease. After death it mum- 

 mifies without decay, and without that 

 efflorescence of spores especially char- 

 acteristic of muscardine and allied 

 diseases. 



The food of healthy insects may 

 become infected by the discharges of 

 diseased larvae, or even, at a consider- 

 erable distance, by the dust of their 

 excrement. The "germs" of the dis- 

 ease may also be introduced by means 

 of accidental punctures of the skin, as 

 larvae crawl over each other with claws 

 soiled with their spore-laden excre- 

 ment. 



Concerning the characteristic para- 



