BY C. .T. POUND, F.R.M.S. XXI 



festations has claimed the attention of the greatest scientific 

 minds throughout the world ; the original manuscripts alone of 

 these investigators would more than fill this room, and yet, 

 although, so much information has heen elucidated in connection 

 with this disease, there still remains practically an inexhaustive 

 field for experimental research work for the most persevering and 

 painstaking of investigators. Not only is tuhercnlosis the most 

 common disease in mankind, but there is no other disease in 

 existence which attacks so numy different kinds of animals. Not 

 one of our domesticated animals is completely refractory to it ; 

 they simply vary in their degree of susceptibility. The first 

 person to claim the honor of having demonstrated the con- 

 tagiousness of the disease was Villemin in 1H65, whose experi- 

 ments were subsequently confirmed by Cohnheim. In the year 

 1HM2 that celebrated bacteriologist Robert Koch, as a result of 

 his masterly and extremely delicate researches with the micros- 

 cope, announced the discovery of the tubercle bacillus, which he 

 succeeded in isolating and cultivating outside the animal body 

 on artificial nutrient media ; further, by inoculating guinea-pigs 

 with small portions of the cultivations, he invariably produced 

 tuberculosis, which caused the death of the animal ; and last 

 but not least, he again found unmistakable evidence of the 

 presence of tubercle bacilli in all the lesions of the disease. 

 These investigations justified Koch in expressing the opinion that 

 "without the tubercle bacilus there could be no tuberculosis — a 

 fact which has been maintained up to the present day. For 

 many years it was generally believed that the blood -serum media 

 as used by Koch was the only one on which the tubercle bacilli 

 could l)e cultivated, but Roux, of the Pasteur Institute, found 

 that a more favourable medium could be found in nutrient agar- 

 agar with the addition of about 6 per cent, of glycerine. On 

 this the bacillus grows abundantly and rapidly ; the growth 

 stands out from the surface of the solid medium and takes the 

 form of small yellowish-white lichenoid grains, which are dry, 

 dense, and difficult to crush, each grain containing hundreds of 

 thousands of bacilli. In the case of liquid media, the growth 

 takes place either at the bottom of the vessel in the form of 

 extremely small yellowish-white grains, development being 



