The Fehrine Corpuscles in the Silhworm. 173 



of animals, in order that tlio classical feature of contagion in an 

 extended area may be better appreciated. 



The silkworm, as is well known, is the larve of the Bomhjx 

 mori, which deposits an ovum, from which, in turn, the caterpillar 

 is produced. The latter, after undergoing four (in some races 

 three) distinct changes of integument, becomes a pupa or chrysahs, 

 and surrounds itself with the silk cocoon. From this, lastly, the 

 perfect moth — imago of naturalists — effects its escape. When it 

 is considered that, in a period of between thirty and thirty-five 

 days, the caterpillar increases in size till it becomes eight or ten 

 thousand times larger than the newly-escaped larve, it will be 

 seen that organic life is displayed with unequalled activity in 

 its development. Diseases, therefore, cannot but progress, pari 

 passu, with an intensity proportioned to the energy of the vital 

 forces. 



In the human economy, of what paramount importance to its 

 conservation are the critical phases of the first and second denti- 

 tion, the arrival of puberty, and the change of the menopause ! In 

 the silkworm no less than seven equally important crises occur, 

 during a comparatively short interval — the cycle of a brief existence, 

 whose momentous stages ofler unusual facilities for the encroach- 

 ment of disease. 



It is to be remarked, if we begin with the earliest phases of the 

 two disorders, that, 



1. Pehrine and sypHiilis are alike 'producible hy artificial 

 inoculation. Pasteur produced a liquid capable of inoculation, by 

 bruising a diseased worm and mixing the mass with a small quantity 

 of water, A number of worms were selected, carefully examined 

 in order to ensure their soundness, and thoroughly cleansed by 

 washing, so that no germs might remain in contact with the skin. 

 He then made a small puncture in one of the posterior rings of the 

 body of each, and inoculated the wound by inserting into it a needle 

 dipped in the infecting liquid. The wounds readily cicatrized, and 

 nothing but a black or dark-coloured spot was soon visible in the 

 site of the puncture. Of twenty worms inoculated in this manner, 

 on one occasion, seven became diseased to such an extent as to 

 exhibit from fifty to two hundred of the corpuscles characteristic 

 of pebrine, in one microscopic field. The experimenter explains 

 why no larger proportion of successful inoculations was made : 

 "The blood which escapes from the wound does not invariably 

 permit of penetration by the corpuscles which are intended to pro- 

 duce infection." Audoin is said to have observed the same fact in 

 his inoculations. Many an experienced physician has failed of suc- 

 cessful vaccination for a similar reason. 



It should be stated, however, that most frequently pebrine is 

 produced by the ingestion of corpuscular germs when the worm is 



