246 



MICROBIOLOGY 



isms isolated from man and from cattle. In 1901 , Koch 4 con- 

 firmed Smith's findings. This led to a number of special 

 investigations to determine the relation between the human 

 and bovine tubercle organisms. The conclusion of these 

 numerous investigations is that the tubercle bacterium from 

 man differs slightly in morphology, in its cultural characters 

 and markedly in its virulence from the bovine variety. This 

 gives us three distinct races of the tubercle bacterium, one in 

 man, one in cattle and one in fowls. 



Tubercle bacteria are found in nature in the tuberculous 

 lesions of man, cattle and other animals suffering with the 

 disease. They are highly parasitic and are not known to exist 

 in nature except as parasitic bacteria. There is, however, a 



Fig. 54. Fig. 55. 



Fig. 54. Bacterium tuberculosis (human) highly magnified. 



Fig. 55. Bacterium tuberculosis (bovine). Drawing from a cover- 

 glass preparation from tuberculous ^tissue of a guinea pig, 

 X about 1000. 



large group of bacteria known as acid- fast or acid-proof or- 

 ganisms, which are found occasionally in the excreta of man 

 and animals and also on timothy hay. They possess staining 

 properties quite similar to the tubercle bacterium. There is 



4 Koch. Amer. Vet. Review, Vol. XXV (1901) p. 441. 



3 One of the most important investigations into the relation 

 between human and bovine tubercle bacteria was by Park and 

 Krumwiede Jr., Vol. V, Research Laboratory, Dept. of Health, City 

 of New York, 1910. 



Also, Jour, of Med. Research, Oct. 1910. 



