The Pebrine Corpuscles in the Silhworm. 175 



the period of incubation previously referred to, a very sensible in- 

 equality was noticeable in these two classes. Those which were left 

 uninfected, displayed unmistakable evidence of greater well-being ; 

 while the diseased worms, when examined by the aid of a lens, 

 exhibited numerous excessively small spots or maculae, hitherto 

 unnoticeable, about the head and rings. These lesions did not at 

 first indicate the presence of the characteristic corpuscles in the 

 skin. The " extension of the latter from centre to circumference 

 had not yet affected the external organs. These surface spots," 

 says Pasteur, "only occur when the internal skin, if I may be 

 allowed the expression, is affected to such a degree as to seriously 

 interfere with the functions of digestion and assimilation." 



Subsequently, however, integumentary lesions were produced 

 which, upon careful examination, were found to contain the pebrine 

 corpuscles. It is difficult to recognize the distinction here esta- 

 blished, and not recall the difference between those superficial 

 syphilides, which disappear readily under appropriate treatment, 

 and those which contain a specific morbid product. One instinc- 

 tively recurs to the theory of Jonathan Hutchinson and others, that 

 the lesions of secondary syphilis are febrile phenomena. These 

 precede the deposits of tertiary forms, in which the " still-born " 

 product of Lancereaux is to be distinguished. 



The patches upon the integument in pebrine are generally of a 

 dark colour, sometimes black (whence the name), some more and 

 some less clearly defined. The petechial character of this stage of 

 the disease has given it the name by which it is known among the 

 Italians (Petechia of the Silkworms). When completely developed, 

 these stains are surrounded by a yellowish areola, which exhibits 

 various gradations in colour. Sometimes they constitute the sole 

 symptoms of the disease. 



M. Quatrefages, with whose opinions Pasteur is not in com- 

 plete accord, declares that the alterations, described above, are 

 best studied in the skin of the young larves. In these he could 

 occasionally descry nothing more than a yellowish tint, slightly 

 obscuring the hyaline transparency of the tissues. Somewhat 

 later, a darker stain became visible, shading gradually into 

 brown, until the translucence of the epidermis was lost. Finally, 

 a brownish-black stigma remained, which was accompanied by a 

 disappearance of all traces of organization. About this, as a 

 nucleus, a yellowish areola extended, which, in his opinion, 

 marked the invasion of the surrounding tissues. This process 

 generally continued until arrested, either by the death of the 

 worm, or by the regular replacement of the old by a new integu- 

 ment. In the course of two or three days, however, the new 

 cuticle, which at first appeared entirely normal, was in its turn 

 affected by the disease, "proving," says Quatrefages, "that the 



