Morphological and Cultural Differences. 507 



Another difference observed between the two types under discus- 

 sion is that in cultures of the bovine type the acidity decreases until the 

 medium at times becomes alkaline, while media containing a growth of 

 the human type, though at first reduced in acidity, becomes more and 

 mpre acid with the age of the culture (Smith). According to Rothhaar, 

 Fibiger & Jensen this characteristic is inconstant. 



These two types of bacilli, however, are not confined strictly to 

 definite species of animals, both types occurring in different species. 

 However, in the great majority of cases tuberculosis of man, dogs and 

 cats is caused by the human type and, tuberculosis of cattle and other 

 ruminants and of swine is caused almost exclusively by the bovine type. 



Tenacity. The tubercle bacillus is extremely resistant to external influences. 

 This is probably due to the waxy capsule by which it is protected. When exposed 

 to the direct rays of the sun they are destroyed in a few hours. In diffuse light 

 they will retain their virulence from 3 to 10 days (Fliigge). In artificial light 

 they are destjoyed in 48 hours (Galtier). Simple drying, especially when imbedded 

 in nitrogenous tissue or fatty medium has little effect on their vitality. Thus in 

 dry sputum protected from light they may remain virulent 126 days (Schill & 

 Fischer), in dry and pulverized tissue from cattle lung 102 days, in large tissue 

 masses 150 days (Cadeac & Malet). Stone found that sputum was infectious after 

 three years. Decomposition affected their vitality very little. Thus decomposing 

 sputum harbors virulent bacilli for six' weeks (Schill & Fischer) and decomposed 

 cattle lung 167 days (Cadeac & Malet). In water, cultures remain virulent 70 

 days, in tissue 120 days. 



The bacilli will remain virulent in raw milk for 10 days (Gasperini) at the 

 end of which period they probably succumb to the influence of lactic acid (Bollinger). 

 On the other hand they have been known to remain virulent 33 days in Emmentaler 

 cheese and 104 days in Cheddar cheese (Harrison). In sweet cream butter they 

 remain virulent 4 weeks. They are destroyed in the course of ten days -in sour 

 cream butter containing 4 to 6% common salt. Sometimes 5 days suffice to destroy 

 them under these conditions (Petterson). On the other hand they have been known 

 to remain virulent 45 days in such butter (Schroeder & Cotton). Treatment with 

 HjOj {" Sudderisierung ") destroys the tubercle bacilli with certainty (Bergman 

 & Hultman). Kefir fermentation does not affect their virulence. 



The influence of high temperatures varies according to the medium in which 

 they are found. Simple boiling or contact with live steam will destroy dry or moist 

 sputum in 5 or 15 minutes, respectively. On the other hand dry sputum can be 

 safely sterilized by the action of dry heat at 100° C. continued for one hour (Schill 

 & Fischer). In milk, bacilli which were originally present as well as bacilli which 

 have been added in cultures, are destroyed in 25 minutes when heated to 65° C, 

 providing the milk was heated in a closed vessel (Forster). On the other hand 

 heating' the milk in open vessels, which does not result in an equal distribution of 

 temperature throughout the mass, will not destroy all tubercle bacilli in the course 

 of six minutes, even if the temperature reaches 80° C. All bacilli found in the 

 film which forms on the surface of tlie milk are more or less protected from the 

 action of the heat (Galtier, Smith, Bang). According to Rabinowitsch & Beck 

 cream can be sterilized by heating for 2 minutes at 85° C. (Herr). According 

 to investigations of Barthel & Stenstrom bacilli will withstand an exposure of 

 80° or 85° C. when the milk is coagulated while they are destroyed in non-coagulated 

 milk at the same temperature. Thus pasteurizing at a temperature of 80° continued 

 for one minute will suffice to destroy the tubercle bacilli providing no coagulation 

 occurs. Freezing temperature of 1° to 8° C. will not destroy the bacilli in 120 

 days (CadSac & Malet). 



With respect to chemical agencies, bacilli occurring in albuminous substances 

 are most effectively destroyed by such chemicals as will not coagulate albumen. 

 Thus carbolic acid 5%, acetic acid 31.8%, or corrosive sublimate 1:1000—500 will 

 not destroy them (Schill & Fischer). Cultures are destroyed in solutions of 0.1% 

 tuberculin in 48 hours, 0.2% methylene blue, 0.1% pyoktannin in 72 hours (Jacob, 

 Bongert & Rosenberg); 0.2% thymol, 4% boraeic acid and 4% creolin or lysol 

 are also effective. Brine and smoke have only a slightly destructive action, virulent 

 tubercle bacilli having been found in tuberculous organs after six weeks immersion 

 in brine (Klepzow). Glycerin acts as a preservative of tuberculous organs (Galtier). 

 Antiformin in solution of 15% does not affect tubercle bacilli or other acid-fast 

 bacilli while non-acid-fast bacilli are destroyed by this agent. On the other hand 

 20% solution of cholin will dissolve the tubercle bacilli at a temperature of 37° 

 to 56°. Neurine is even more effective (Deycke & Much). 



