190 BACILLUS TUBERCULOSIS. 



that on blood-serum, but occurs much more rapidly. In the 

 course of time the whitish color is replaced by a light ochre- 

 yellow. The growth soon spreads to form a heavy dry film 

 which covers the entire surface of the medium and at times 

 extends up the sides of the tube for a short distance. 



When transplanted into veal-bouillon, or glycerin-veal-bouillon, 

 a membrane resembling that seen on solid media is formed. A 

 characteristic of the growth in fluid media is that develop- 

 ment is limited to the surface, leaving the medium perfectly 

 clear. The tubercle bacillus requires oxygen for its growth, 

 and therefore will not grow beneath the surface of the culture. 



Cultures may also be made on potatoes which are partly 

 submerged in a 5 per cent, glycerin and 0.5 per cent, sodium 

 chloride solution. A heavy film is formed on the potato and 

 on the surface of the glycerin and salt solution. The fluid 

 remains unclouded. Still another medium on which the 

 tubercle bacillus can be grown is a mixture of commercial 

 ammonium carbonate, 5 per cent. ; primary potassium sul- 

 phate, 0.15 per cent.; magnesium sulphate, 2.5 per cent; 

 glycerin, 1.5 per cent. 



Vitality of the germ : A ten-minute exposure to a tempera- 

 ture of 70 C. kills the germ ; 95 C. is fatal in one minute. 

 It is not affected by cold. Direct sunlight is fatal in a very 

 short time, depending on the amount of material exposed. 

 This effect on the germ of the sun's rays is now being made 

 use of in the treatment of tuberculosis. Patients are exposed 

 to the direct rays of the sun in so-called " sun parlors" for as 

 long a time during the day as possible ; or exposure is made 

 to the concentrated rays for a short time. The supposition 

 is that the germ will be either destroyed or inhibited in its 

 growth, and that the system will thus have an opportunity to 

 overcome the infection. The germ resists diffused daylight 

 for a week or longer. Desiccation at ordinary temperatures is 

 also resisted for a long time. Dry heat kills more slowly 

 than moist heat. Bacteria placed in water at a temperature 

 of 95 C. are killed in one minute, whereas dry heat at a 

 temperature of 100 C. is often ineffective after an exposure 

 of several hours. The bacilli contained in tubercular sputum 

 are killed by a 3 per cent, solution of carbolic acid in about 



