230 DR. KLEIN. 
sponding to each successive period in the development of the 
pustule, which had been removed from the animal in a per- 
fectly fresh state. With the aid of the complete and con- 
tinuous series of preparations of which I thus became 
possessed, I was enabled to study the process in a most satis- 
factory manner. 
The lymph used for inoculation was obtained from two 
sources, one quantity having been sent to me by Professor 
Chauveau, of Lyons, the second by Professor Cohn, of 
Breslau. In some of the inoculations the lymph was first 
diluted with from fifteen to twenty times its volume of 
half per cent. solution of common salt; in others it was used 
undiluted. No difference was observed as regards the results 
between the diluted and undiluted liquids; in all cases 
the instrument employed for insertion was a Pravaz syringe. 
A drop having been drawn into the steel canula of the 
instrument (the width of which does not exceed the fortieth 
of an inch), it was passed under the surface of the skin, as 
in subcutaneous injection. In order to avoid bleeding, great 
care was taken to direct the needle in such a way that 
it penetrated the true skin as little as possible. Before 
discharging it the canula was always slightly drawn back, so 
as to leave the channel previously made by its point free for 
the reception of the expelled liquid. It will be understood 
that in using a subcutaneous syringe for inoculation in the 
manner above described, the only part of the instrument which 
is occupied by the liquid to be inserted is the extremity of 
the steel tube; the extremely small quantity of liquid which 
is thus employed is ejected at the desired moment by the 
compression of the air behind it. 
Although there can be no doubt that the nature of the 
pathological process in the skin is the same whether it is 
determined by the direct insertion of the virus into the 
affected part, or is conveyed to it by the circulation, yet it 
appeared clear that the value of the results would be impaired 
if the investigation extended only to the local effects produced 
by inoculation. I therefore felt it to be very desirable (con- 
sidering it was out of the question to obtain opportunities of 
studying the disease as it occurs naturally) to induce it in a 
form resembling the natural one as closely as possible. 
Natural sheep-pox, as acquired by the ordinary modes 
of infection, is characterised by a general eruption, the 
first appearance of which is accompanied by an accession 
of fever. 
I had not only learned from my own observation that no 
general eruption could be induced by inoculation, but found, 
