BUREAU OF ANIMAL INDUSTRY. 611 



more or less resistant, according to circumstances, and whicli is more 

 resistant in the animal tissues than in cultures. 



Microscopical characters, however, are now and then misleading, 

 unless we intorj^ret them by physiological experiments. _ Judging 

 from what has hitherto been considered properties of bacterial spores, 

 the microbe of hog-cnolcra cannot lay any claim to the production 

 of true endogenous spores. Their absence is determined by results 

 of experiments recorded in the i)receding pages : 1. The thermal 

 death-] )()int of the bacterium at 58" C. An exposure to this tempera- 

 ture ior 15 to 20 minutes destroys not only the vitality of cultures of 

 all ages, but also the dried germ in the tissues of the infected animal. 

 A momentary exposure to boiling water is equally efficacious. 2. 

 The bacteria are destroyed by disinfectants in solutions which are 

 incapable of destroying spores. 3. They are killed by simple drying 

 far more quickly than are spores; at the same time their resistance to 

 drying is much greater than might be expected under the circum- 

 stances. In the experiments recorded some dried bacteria in spleen 

 pulp were killed in less than a month; others resisted forty-nine days. 

 We may put the limit, which is very much less for dried cultures, be- 

 tween one and two months. It is this continued vitality in the dried 

 state that suggests the existence of a membrane which is more re- 

 sistant than that possessed by the great majority of bacteria in their 

 vegetative state. This difference between bacteria in the vegetative 

 an the spore state is illustrated by the anthrax bacillus. In cultures 

 the bacilli are killed by drying in five or six days; the spores, under 

 the same condition, retain their virulence for years. 



All the facts brought out by the study of this bacterium lead to the 

 conclusion that a distinct spore state, so called, does not appear either 

 within the animal body or in nature. * 



Observations on the pathogenic ^jroperties of the bacterium of 



hog-cholera. 



In addition to the foregoing experiments on the general biological 

 characters of the bacterium of hog-cholera, a few additional obser- 

 vations were made upon its pathogenic activity, with a view to deter- 

 mine more precisely the mode of infection. 



Groiuth m vacuo. — It seemed desirable to learn the extent to which 

 the bacterium wsls capable of multiplying with a minimum supply of 

 oxygen. The following simple experiment was tried: 



An elongated glass bulb of about 15'^'^ capacity, terminating in a narrow tube 

 about 10'^'" long, and containing about 5'=<= of beef -infusion peptone, was inoculated 

 from a ])ure culture. The air was then exhausted by an air-pump for fifteen min- 

 utt's, while the bulb was kept immersed in a water bath at a temperatiu-e of 38° C. 

 It was finally sealed in tlie flame and placed in the incubator. The results of three 

 separate experiments were practically the same. In the bulbs the culture liquid was 

 turbid on the following day. This turbidity increased but slightly, and within tluree 

 or four days growth liad evidently ceased. Four other microbes, two of wliich were 

 found in the exudates of swine-plague bacillus luteus described in the Second An- 

 nual Eeportpf tlie Bureau, a micrococcus, bacillus subtilis, and a microbe producing 

 septica'mia in rabbits, were treated in the same way. None of the tubes became 

 turbid. When, after tlu-ee or four days, the bulbs were opened and filtered and air 

 allowed to enter, the Uquids became tm-bid witlun twenty-four hours, the charac- 

 teristic pigment of the bacillus luteus appearing a few days after. 



* There is no reason why the bacterium in the body of animals may not be in an 

 arthro-sporous state, according to the classification of de Bary. The name is of little 

 account as long as we define the properties belonging to a given state. 



