1893. CORRESPONDENCE. 399 
when he began to feel old. His wife died some years ago, but he 
leaves two sons, to one of whom, Casimir, we have already referred 
as a well-known botanist. 
E regret to announce the death of the Rev. T. Wolle, pastor of 
the Moravian Church at Bethlehem, Penn. He was the author 
of books on the Fresh-water Algae of the United States and on the Desmids 
of the United States. His work has value as that of a systematic 
pioneer and recorder of forms—a labour to which he brought great 
zeal and enthusiasm. 
ROFESSOR Giuseppe Antonio Pasquale, who died at Naples on 
February 14, was Professor of Botany at the University, and 
Director of the Botanic Gardens. He was the joint author of a 
‘¢ Flora medica della Provincia di Napoli,” published in 1841, anda 
‘‘Compendio di Botanica,” which reached a third edition in 18go, 
He also wrote an account of the ‘‘ Flora Vesuviana,’’ and other 
systematic and morphological papers, and compiled a ‘‘ Catalogo del 
real orto botanico di Napoli.” 

CORRESPONDENCE. 
I HAVE to thank Dr. Hurst for bringing to my notice his interesting suggestion 
as to how inoculation may be supposed to confer immunity from disease. The idea 
that the attenuating process produces, by selection, a new strain of microbe having a 
different physiological action, seems worthy of careful examination. Such a gradual 
production of a more slowly-increasing variety well explains the diminishing intensity 
of the disease produced by successive inoculations. As Dr. Hurst points out, the 
diapedesis of the leucocytes is soonest able to overcome such feebly-increasing 
organisms. There is, however, to my mind, this difficulty. Attenuating processes 
consist generally in growing under unfavourable conditions, and I cannot see why 
such conditions should favour the slowly-increasing rather than the rapidly-increasing 
varieties of the microbe. Indeed, it seems to me probable that, other things being 
equal, unfavourable conditions generally would rather select the more quickly- 
increasing. Quick breeding is such an obvious advantage under adverse circum- 
stances, as affording, in each generation, more numerous chances of survival. 
There remains, of course, the suggestion that the selection may ‘‘act in some 
other way.” 
Supposing, then, we have a virus attenuated in the manner suggested by Dr. 
Hurst, how can immunity conferred by inoculation with the same be explained ? 
We may take it as an established fact that the local inflammation attending 
inoculation is accompanied by diapedesis of the leucocytes. These leucocytes, in 
their abnormal state of activity consequent on inoculation,—and, perhaps, as Dr. 
Hurst suggests, in increased numbers,—and, after their victory over the feebler 
army of microbes, might be ready to attack and subdue the more formidable foe. 
This would explain momentary immunity, but I cannot see how such a state of 
