270 MICROBES, FERMENTS, AND MOULDS, 
be necessary and sufficient, quantities which vary 
according to circumstances. In order to vaccinate 
a sheep against anthrax, the animal must be held by 
its fore feet in a sitting position, so as to present its 
belly to the operator; the tube of a Pravaz syringe, 
containing the injection, is then inserted in the base 
of the groin, which is devoid of wool. In cattle the 
operation is performed at the root of the tail. It is 
performed twice—first with a weak vaccine, and, after 
the lapse of a week, with one which is stronger. 
Every one is acquainted with the process of vacci- 
nating the human subject against small-pox, which 
may be done either with lymph from an infant or 
from a calf. A lancet or grooved needle is employed, 
on which there is a drop of lymph, and five or six 
punctures are made on the arms or thighs. 
We must not imagine that vaccination can become 
an absolute preservative from all diseases. For in- 
stance, in erysipelas, pneumonia, and gonorrhoea 
a first attack is so far from warding off a second 
attack of the same disease, that it creates a favourable 
field for relapses. It may, consequently, be assumed 
a priort that vaccination in such cases would do more 
harm than good (Cornil). It is the same with inter- 
mittent fever, tuberculosis, syphilis, etc.; all diseases 
by which the same individual may be attacked several 
times, and at varying intervals of time—a clear proof 
that the first attack has created no immunity against 
subsequent attacks. 
