582 
NATURE 
[ Oct. 14, 1886 
Infectious pneumo-enteritis of the pig (swine fever) has been 
shown by Dr. Klein to be caused by the introduction into the 
body of the affected animal of a specific bacillus. This disease 
among pigs is highly infectious, the contagium being transmis- 
sible from pig to pig through the air, and per-isting in infected 
buildings in a similar manner to the observed behaviour of small- 
pox and scarlet fever among human beings ; and, though not 
transmissible to mankind, it can be inoculated upon rodents, 
although in the latter animals it is not contracted by infection 
received through the air. 
The experiments on the disinfecting power of dry heat were 
mostly made in a copper hot-air bath, or in one improvised of 
flower-pots, and furnished with a Bunsen’s regulator ; those with 
steam were made in a felt-covered tin cylinder, through which 
passed a stream of steam from a kettle beneath. 
The mode of procedure in exposing the materials to heat was 
as follows :—Strips of clean flannel were steeped in the respec- 
tive infective fluids, dried in the air, wrapped separately and 
loosely in a single layer of thin blotting-paper, and suspended 
in the centre of the apparatus in company with a thermometer, 
so placed that its bulb was close to the packets of infected 
material. 
The following were the results of the experiments with dry 
heat :— 
Anthrax bacilli without spores were sterilised by exposure 
for five minutes only toa dry heat varying between 212° and 
218° F, 
Spore-bearing cultivations of the bacillus anthracis, on the 
other hand, did not lose their vitality by a two hours’ exposure 
to 220° F., but were sterilised by exposure for four hours to 
220° F., or one hour to 245° F. 
A rabbit inoculated with swine fever virus which had been 
exposed to dry heat varying between 212° and 218° F. for an 
hour remained well; but one inoculated with virus exposed to a 
similar heat for only five minutes, died of swine fever after nine- 
teen days, the usual time of death after inoculation being between 
five and eight days. 
Guinea-pigs inoculated with tuberculous pus exposed for five 
minutes to 220° F. remained well. 
The foregoing results, as far as regards anthrax, are far more 
favourable to the efficacy of dry heat as a disinfecting agent than 
those of Koch. It appears that the spores of the bacillus an- 
thracis lost their vitality, or at any rate their pathogenic quality, 
after exposure for four hours to a temperature a little over the 
boiling-point of water, or for one hour to a temperature of 245° F. 
Non-spore-bearing bacilli of anthrax and of swine fever were 
rendered inert by exposure for an hour to a temperature of 212°- 
218°, and even five minutes’ exposure to this temperature sufficed 
to destroy the vitality of the former, and impair that of the latter. 
As none of the infectious diseases for the extirpation of which 
measu-es of disinfection are in practice commonly required are 
known to depend upon the presence of bacilli in a spore-bearing 
condition, it is concluded that, as far as our present knowledge 
goes, their contagia are not likely to retain their activity after 
being heated for an hour to 220° F. 
In the experiments with steam the results were conclusive as 
to the destructive power of steam at 212° F. upon all the con- 
tagia submitted to its action. In one instance only was there 
room for suspicion that the disinfection had not been complete : 
this was in the case of the highly-resisting anthrax spores, 
exposed to steam for five minutes only : the animal had six days 
afterwards a swelling at the seat of inoculation, but remained 
well. On the other hand the animals inoculated with unheated 
portions of the same materials all died. 
These results are in accordance with those of Koch, Gaffky, 
and Loffler, and it may be considered established that the com- 
plete penetration of an object by steam heat for more than five 
minutes is sufficient for its thorough disinfection. 
In view of the above satisfactory results it was not deemed 
necessary to make any experiments as to the disinfecting power 
of steam at higher temperatures or under pressure, its efficacy 
being taken for granted. 
Dr. Klein found that boiling in water for only one minute was 
sufficient to render inert the spores of the bacillus anthracis, 
although it is known that some of the spore-bearing non- 
pathogenic bacilli are only destroyed by prolonged boiling, or by 
a moist temperature above the boiling-point. 
Some observations were made on the destruction of lice by 
heat. It was found that the eggs of lice could be conveniently 
hatched by tying up tightly in muslin a small piece of the gar- 
ment on which they were deposited, and carrying it about for a_ 
week or two in a warm pocket. Tested in this way no develop-— 
ment was found to take place in eggs of lice which had been — 
exposed for one hour to 300° F. dry heat, for one hour to | 
230” F. dry heat, or for ten minutes to steam at 212° F., or which 
had been boiled for five minutes in water. The maximum heat — 
which lice or their eggs will bear with impunity was not 
ascertained. 
In order to secure the thorough and certain disinfection byd 
heat of porous articles likely to retain infection, such as clothing — 
and bedding, it is necessary that the heat should be made to— 
permette the articles in every part to such a degree and for such 
a length of time as to destroy all infectious matter which they 
may contain. 
It has been remarked that such articles as bedding and blan- 
kets are the highest outcomes of the ingenuity of man to check 
the passage of heat. from one side of the object to the other. Tt 
is no wonder, therefore, that they should be found difficult of 
penetration by heat. Even thin layers, however, of badly con-. 
ducting substances interpose a considerable barrier to the passage 
of dry heat. The following experiment was made to ascertain 
how far the inclosing of infective objects in blotting-paper or 
test-tubes plugged with cotton wool (as in Dr. Koch’s experi- 
ments) hindered the full access of heat to them. 
Two similar registering thermometers were taken: the bulb | 
of one was tied up in a single layer of thin white blotting-paper, _ 
that of the other was placed in a test-tube 3 inch wide in such a 
manner as not to touch the sides, and a plug of white cotton 
wool I inch deep was pushed into the tube around the stem of 
the thermometer, but not as far as the bulb. Both the paper 
and cotton wool were previously dried. The two thermometers, 
together with another with bare bulb, were then husg up in a 
hot-air bath. Heat being applied, the thermometers were read. 
half-hourly as follows :— 7 
Readings of thermometer with bulb 
Time from lighting Bare In psper In tube 
os 3 F. 
4 hour 162 147 15! 
1 hour 212 193 196 
thhour ... 234 213 219 
2 hours 242 236 eS 238 
2k hours... 244 ne 244 200 244 
The following experiment was made with a thermometer having 
the bulb covered with a single layer of blanket and placed in the 
hot-air bath already heated :— 
Thermometer Thermometer 
aime inomsplacine an with bulb with bulb 
hot-air bath bare tay blanket 
4 hour 246 231 
1 hour 260 250 : 
14 hour 266 254i ; 
2 hours ae 268 263 
24 hours we 268 264 “4 
Experiments made with larger articles and apparatus showed 
how difficult it was to secure the penetration of a dry heat suffi- 
cient for disinfection into the interior of such an object as a 
pillow. It was only effected by employing a high degree of 
heat, or by continuing the exposure during many hours, length 
of exposure compensating for a lower degree of heat. On the 
other hand heat in the form of steam penetrates much more 
rapidly than dry heat. Thus a thermometer in a roll of dry 
flannel placed in a hot-air bath at 212° F., at the end of an hour 
registered only 130° F. In the same roll, placed in the steam 
cylinder for ten minutes, the thermometer marked 212° F.  Ex- 
periments on the large scale were equally conclusive. The causes” 
of the superior penetrative power of heat in the form of steam 
over hot air appear to be :— J 
(1) The large amount of latent heat in steam, set free on its 
condensation. In hot dry air, on the other hand, the evapora- 
tion of hygroscopic moisture takes up heat and delays the attain- 
ment of the required temperature. 7 
(2) Steam, on condensation into water, occupies but a ver 
small fraction of its former volume and thus makes room for 
more. Hot air in cooling diminishes in volume in much les 
proportion. 4 
(3) The heat evolved in the moistening of a dry porous sub- 
stance. In the centre of a highly-dried roll of flannel pla 
in the cylinder in acurrent of steam at 212° F., a thermometer, 
after five minutes’ exposure, registered 239° F. 
