VIRUS OF SHEEP POX. 
35 
matter, the disease being before him in an unfavourable form, he 
operated with the virus that presented itself in the sheep already 
labouring under the disease, and in a fortnight repeated the inocu- 
lation on such sheep as had not taken the disease. In August 
following, from pustules resulting from repetition of inoculation in 
sheep, he inoculated on another farm — it being his annual inocula- 
tion — 108 lambs. The result was, that of the 400 sheep he lost 
forty, and of the lambs twenty. The loss of the sheep might have 
admitted of explanation on the score of the unfavourable turn the 
disease now and then will take in spite of us ; but how came it that 
the lambs, in another situation, and where all others had done well 
in former times, should likewise die 1 It was owing to the dele- 
terious virus employed ; and this affair it was that first disabused 
M. Lebel about indifference of the choice of matter. 
There needs no further proof of the contagious property of mat- 
ter of sheep-pox, be it the product of malignant or benign pox; 
but it becomes a question, whether or not this property, especially 
in the latter, does not become weakened under successive inocula- 
tions. Hurtrel d’Arboval is of opinion that it becomes so after the 
fifth time of inoculation. “ For my own part, however/' says M. 
Lebel, “ I would say rather the fifteenth time.” 
In May 1846, M. Lebel inoculated fifty lambs, the produce of 
the year. The beginning of June — every thing having proceeded 
favourably up to that time — sixty-eight fresh-purchased sheep, of 
ages from one to three years, were turned to run with the flock 
that the fifty lambs had rejoined. From twenty to twenty-five 
days afterwards — from thirty-six to forty days since the inocula- 
tion of the lambs — some of the new-comers exhibited proofs of 
infection : twenty of them had got the pox, some confluent, some 
benignant. Those of the sixty-eight who had not caught the dis- 
ease Lebel inoculated from the others. 
This fact establishes the conservative as well as the infective 
properties of the virus. And, further, the matter Lebel used on 
the occasion is the same as has served him for upwards of ten 
years . Nor has he, since November 1840, had any natural pox 
virus : and such is the difficulty, not to say impossibility, to collect 
matter from natural pustules, that Lebel has not troubled himself 
about it, but has contented himself with what he had in possession. 
M. Lebel does not, however, deny that the disease, through so 
many transmissions, undergoes some mitigation, seeing that lambs 
which he is inoculating year by year with virus which he has bv 
him, experience hardly any derangement of health while the dis- 
ease is on them, and that it is rare for him to lose more than one 
in a hundred. 
Another question is, what stage ought the inoculated pox to 
