BACTERIAL DISEASES OF THE ANIMAL KINGDOM 121 



only species that exhibits this peculiarity with regard to stains, though 

 the number of such organisms is not great. They are classed together 

 as "acid-fast bacteria." Much research has been undertaken to find 

 out the peculiarities of growth, etc , of the acid-fast bacteria, in order to 

 be able to distinguish them readily from Bac. tuberculosis, so as to 

 facilitate the diagnosis of the latter. Most of these bacteria have been 

 obtained from sources outside the body, hence, if the material under 

 observation has been derived from the latter source, and yields an 

 acid-fast bacillus, the probability of this microbe being Bac. tubercu- 

 losis is very great. 



The animal body is the natural feeding-ground of this germ, in 

 which alone it can multiply. Infection takes place almost exclusively 

 through the air. The sputum of a consumptive patient contains large 

 numbers of these bacteria, and when the sputum dries up they are 

 conveyed by the atmosphere to other places. The resistance power of 

 the bacilli is very great. In a dry condition they are virulent even 

 after two months' exposure to the air, and even in a moist condition 

 their vitality is not impaired for several weeks. Hence, whether in the 

 dry or in the moist condition, the danger from these germs is not over 

 for a long time after their liberation from the body of a tuberculous 

 patient. Another point worth noticing is that these bacilli have been 

 found in a live condition in tubercular organs many weeks after the 

 latter have been buried. It is not surprising, therefore, that the 

 bacillus of consumption does not visit us in the form of an epidemic, 

 but rather attacks one here, another there, according as it finds a suit- 

 able medium for its growth and multiplication. The germs are present 

 in most places, but are naturally in greater number in crowded towns. 



The poison secreted by Bac. tuberculosis is not well known, but its 

 existence is made evident by the effect that Koch's tuberculin has on 

 human subjects. Tuberculin is a concentrated glycerin-bouillon-culture 

 of Bac. tuberculosis. After sterilisation of this culture it was found 

 that 0*25 c.c. of the liquid caused a healthy man, after three or four 

 hours, to suffer from malaise, laboured breathing and a tendency to 

 cough, all of which, however, passed off after 24 hours. Tuberculin 

 was introduced by Koch as a curative agent on the same principle as 

 vaccination for the prevention of small-pox. Unfortunately, it has not 

 been successful, neither can the same be said of the new tuberculin 

 which was introduced by him in 1897. 



To this group must also be reckoned Bac. anthracis, which fortu- 

 nately does not often attack man. The disease is known as Anthrax 

 or Malignant Pustule. The bacillus multiplies rapidly in the blood, 



