THE INFECTIOUS DISEASES. 223 



If cultures of tbe anthrax bacillus be made at a temperature of about 42 C. 

 growth occurs, but it is meagre. Spores are not formed as they are at body tem- 

 perature, and the virulence of the germ diminishes day by day, so that at last the 

 most susceptible animals are not affected by large inoculations of the living organ- 

 isms. If fresh cultures of these organisms be made in various stages of their 

 diminishing virulence and maintained at their optimum temperature, spores will 

 again form, the growth will become vigorous, and in morphology quite character- 

 istic; but the physiological qualities which determine virulence will remain more 

 or less in abeyance. 



By inoculation of animals with anthrax cultures, beginning with those which had 

 been maintained at 42 C. for from fifteen to twenty days, and thus possessed but feeble 

 virulence, and passing to those cultivated at 42 C. for a shorter time and which were 

 therefore more virulent, Pasteur was able to secure immunity from anthrax in a series 

 of the lower animals (see page 174). Based upon these experiments a method of pro- 

 tective inoculation has been practised on a large scale among sheep and other animals 

 in some parts of Europe which has been of great economic value. According to some 

 authorities the death rate from anthrax has under these preventive inoculations been 

 reduced in sheep from ten per cent to about nine-tenths of one per cent, and in cattle 

 from five per cent to less than four-tenths of one per cent. 



ACTINOMYCOSIS. 



This disease, which is of occasional occurrence in man, but is more 

 common in the domestic animals, especially in cattle and in horses, is 

 most frequently characterized by a slow suppurative and proliferative 

 process, often leading to the formation of large fungous masses which 

 may become calcareous. 



In cattle the new-formed tissue, which develops with especial fre- 

 quency in the jaw, is apt to extend beyond the original site and to 

 slough, so that not only may the tissues of the tongue, pharynx, larynx, 

 etc., be involved, but secondary nodules of similar character may form 

 in the lungs, gastro-iutestiual tract, and skin. 



In man suppuration with necrosis and the formation of abscesses, 

 ulcers, and fistulse, are the most marked lesions in parts near the surface 

 of the body. In the lungs the lesions may be essentially those of an 

 acute general bronchitis or in the form of broncho-pneumonia (Fig. 

 107), with the formation of new tissue. 1 



Abscesses and cavities may form which extend into adjacent parts. 

 In intestinal actinomycosis nodular masses of new tissue with ulceratioii 

 may develop in the mucosa and submucosa. Metastases have been de- 

 scribed. The excitant of this disease now most commonly called Strep- 

 tothrix actinomyces or. Actiuoinyces bovis is a micro-organism which 

 seems to be more closely related to the moulds than to the bacteria. It 

 is, however, considered here because its botanical position is not yet 

 clearly established, and it is still commonly regarded as one of the so- 

 called pleomorphous or "higher bacteria" (see page 145). 



The organism often grows in the tissues in the form of little rounded 

 masses from a size so small as to be invisible to that of a pin's head. 

 They may be transparent or grayish-white or yellow or dark in color. 



1 For a detailed description of the lung lesions in actinomycosis, with general bib- 

 liography, see Hodenpyl, " Actinomyosis of the Lung," New York Medical Record, De- 

 cember 13th. 1890. 



