458 THE TUBERCLE BACILLUS GROUP 



tubercle bacilli; the spontaneous disease, however, is almost invariably 

 an infection with the bovine type of the tubercle bacillus. 1 



The most common initial lesion in cattle is an involvement of the 

 retropharyngeal glands; the lungs are frequently infected, and occa- 

 sionally the liver and serous membranes are invaded rather early in 

 the disease. A peculiar and characteristic type of infection of cattle, 

 known as Perlsucht or pearly disease, which progresses slowly and is 

 recognizable only in the later stages, is distinguished by the occurrence 

 upon serous surfaces of thick fibrous tumors containing much con- 

 nective tissue. The lesions in infections of the peritoneal surfaces 

 consist of large numbers of solitary or clustered tubercles varying in 

 size from 1 to more than 10 mm. in diameter. They may be attached 

 to the surface by tough, fibrous pedicles or they may rest directly upon 

 the membrane itself. These tumors may become calcified or caseated 

 and they are larger than tubercles found in human tissues. Morpho- 

 logically their structure is fundamentally not unlike human tubercles. 



Theobald Smith 2 was the first to clearly point out the differences 

 between the human and bovine tubercle bacilli. His evidence was 

 based upon morphological, cultural and pathological characters. He 

 showed that the human tubercle bacillus, grown on serum, was longer 

 and slenderer than the bovine type and frequently curved. The 

 growth is more luxuriant, forming a thick, wrinkled membrane upon 

 glycerin broth. The bovine type commonly develops feebly in this 

 medium and produces a thin, delicate pellicle. The reaction curves 

 of the two types on glycerin broth are distinctive and characteristic. 

 The bovine type gradually creates an alkaline reaction; the human 

 type leaves the reaction acid and tuberculin made with the bovine 

 type consequently is alkaline in reaction; that of the human type is 

 acid. The pathogenic action of the two types is distinctive; the 

 bovine type is highly pathogenic for rabbits and calves; the human 

 type is only slightly pathogenic for these animals. One milligram of 

 a human culture fails to kill rabbits, but 0.1 milligram of a freshly 

 isolated bovine culture results fatally. 



The important differential characters are summarized in the follow- 

 ing table: 



HUMAN TYPES. BOVINE TYPES. 



MORPHOLOGY. 



On serum or glycerin bouillon, long, On serum or glycerin bouillon, rela- 



slender, slightly curved rods which lively short thick rods irregularly ar- 

 usually stain uniformly; occur in clusters - ranged; frequently exhibit slight irregu- 

 usually lying parallel. larity in staining. 



1 Theobald Smith, Boston Medical and Surgical Journal, 1909, clix. 707. 



2 Jour. Exp. Med., 1898, iii, 451. 



