449 



granules of Viallanes, as described in his admirable memoir on the 

 histolysis of insects."* He, however, does not discuss their nature, 

 simply speaking of them as the ever present and unmistakable symptom 

 of the disease either in the silkworm or other larvre upon which he had 

 experimented.! Professor Forbes, however, shows no evidence of hav- 

 ing seen the several Italian articles of which I have spoken, but devotes 

 his attention to the bacterial causes of the disease, causes which theEuro- 

 pean investigators have either overlooked or ignored. Bolle regretted, 

 in the comprehensive article from which I have quoted, that the inac- 

 curate nature of microchemical research prevented his advancing any 

 well supported theory on the exact nature of these globules, though he 

 intended pushing his studies further. I can not find that he published 

 any later article thereon. The tests which he used in endeavoring to 

 determine their chemical composition are such as would be used at this 

 day, so that we need hardly look to any newly discovered chemical 

 processes to aid us in new researches. 



For the cause of grasserie as many theories have been advanced as 

 there are writers on the subject. Among those apparently the more 

 reasonable are that it may be caused by a disturbed digestion (Lomeni) ; 

 by '• close, damp heat, accompanied by electrical tension, or by a sud- 

 den change in the pressure of the atmosphere'' (Maestri)^ by "damp 

 air and lack of ventilation, light, and cleanliness " (Oornalia) 5 or by 

 the manner of preserving the eggs or the influence of some hereditary 

 predisposition (Haberlandt). Pasqualis calls attention to the fact 

 that had come to his notice that near Venice, where the trees are 

 annually pruned, grasserie is much more common than around Trent, 

 where the food is picked from old wood. He therefore ascribes the 

 trouble to the feeding of too tender leaves. It will be recalled that 

 my report for 1SS9 mentioned the fact that all of our brood, fed on the 

 tender leaves of a trimmed osage orange hedge, died of grasserie, while 

 the brood fed in the same room, on mulberry leaves picked from old 

 wood, gave such remarkable results as 135 pounds of cocoons per ounce 

 of eggs. The latter showed very few cases of grasserie. I once asked 

 Maillot his opinion of the cause of the disease and he attributed it to 

 too rich food, saying that often a worm just ready to spin would eat an 

 especially rich leaf and be attacked by the disorder. To this phase of 

 the subject I shall recur later. 



So far as I can venture an opinion on this subject it seems to me 

 that Professor Forbes has come nearer to the true cause of the disease, 

 which he considers bacterial. He states, however, in his publications 

 on the subject, that he worked under the disadvantage of not seeing 

 the brood of silkworms that had been attacked by the disease, but 

 began his researches on some dead, though fresh, larvre which had 

 been sent to him bv Professor Burrill of the Illinois Industrial Uni- 



'Aun. Sci.Nat. Zool., xiv, 1, Arf. 1, August, 1882. 

 tXotablythe cabbage worm iPieris rapa^). 



