CHAP, xiii PATHOGENIC BACTERIA IN MILK 223 



neck of 50 milligrammes of a culture under three weeks old 

 a culture of bovine tubercle does not produce progressive 

 bacilli not older than three tuberculosis in the animal, nor 

 weeks produces generalised does it kill it. In the majority 

 tuberculosis, starting from the of instances the inoculation re- 

 point of inoculation and end- suits in the formation of a local 

 ing fatally, usually within lesion." i This becomes retro- 

 eight weeks." ^ gressive and localised. 



Eabbits. — Highly pathogenic. Only slightly pathogenic. 



Intravenous inoculation of " Intraperitoneally and sub- 



O'Ol to 0-1 mg. or intra- cutaneously injected into rabbits 



peritoneal injection of O'l to the human tubercle bacillus pro- 



1 '0 mg.causes acute and rapidly duces lesions which are scattered, 



fatal tuberculosis. or localised, or retrogressive." ^ 



Ghimpanzee and Monkey. — Acute Similar to the bovine type, 

 tuberculosis produced by very 

 small doses. 



An additional distinguishing test, introduced by Theobald 

 Smith, is the amount of acid production in glycerine broth. 

 Smith found that after a fairly vigorous growth has been estab- 

 lished on glycerine broth the bovine type will convert a bouillon 

 containing 5 per cent glycerine and of a certain degree of 



acidity to phenol-phthalein (2 per cent ^r-acid) into an alkaline 



medium. At the end of one to two months the solution is 

 alkaline. The acidity of some types reaches 4 per cent of a 

 normal solution ; that of other types but !• 5 to 2'0 per cent." 

 The human type does not do this. At the end of one to two 

 months' growth in the bouillon the solution is acid. 



The acidity reaction in glycerine broth has not been 

 accepted by all workers as a reliable differentiating character, 

 but Theobald Smith, who first clearly differentiated the two 

 types of tubercle bacilli, finds it of great value and constancy. 

 He remarks : " After a trial of seven years I find the acid 

 or alkali production of different strains, under cultivation 

 from one to fourteen years, constant." 



To distinguish the type of tubercle bacillus present in any 

 given material the most convenient and practical tests to employ 

 ■ are the quantity and nature of the growth on glycerine agar 

 and in glycerine broth and the rabbit virulence test. Guinea- 

 pigs are inoculated with the material under investigation, and 



^ Royal Tuberculosis Commission, Final Eeport, 1911, pp. 4-6. 

 ^ Sixth International Congress on Tuhcreulosis, 1908, iv., part i. p. 651. 



