378 INFECTIVE DISEASES. 



can be revealed either by microscopical examination of the suspected 

 tissue, or after inoculation in guinea-pigs. 



Bacillus Tuberculosis (Koch). — Rods, 2 to 4 ju, and occa- 

 sionally 8 ij. long, very thin, and rounded at the ends. They are 

 straight or curved, and frequently beaded, and occur singly, in pairs, 

 or in bundles ; there are also involution forms and short branched 

 threads. Spore-formation is observed in old cultures. They are 

 non-motile. Tn the interior of giant cells they are often accompanied 

 by grains which exhibit the same colour reaction. 



The bacilli in tissue sections of bovine tuberculosis are shorter 

 and less granular than those in human tubercular sputum, but in 

 milk they are quite as long, and even longer, and very distinctly 

 granular or beaded, and are thus brought much closer, morpho- 

 logically, to the bacilli in human sputum. Speaking generally, 

 however, the average length of the human bacilli is greater than 

 the average length of the bacilli in cow's milk, but the longest of 

 the bovine bacilli cannot be distinguished in length from the longest 

 human bacilli. There are, however, exceptional cases, for in some 

 preparations of pus from human lungs the bacilli are remarkable, 

 not only for their thinness, and their uniformly beaded character, 

 but more particularly for their extraordinary length. They should 

 be compared with other preparations, in which the bacUli, though in 

 human sputum, are sometimes much more distinctly rod-shaped, 

 much shorter and thicker, with complete absence of any beaded 

 appearance. Neither length nor granularity is a characteristic 

 sufficient to denote any specific difference between human and bovine 

 bacilli. The author has examined minutely the bacilli in tuberculosis 

 of other animals, such as the horse, pig, and cat ; and of birds — the 

 fowl, guinea-fowl, pheasant, and ostrich. Here, again, minute 

 morphological differences can be observed. For example, in many 

 cases in fowls the bacilli are conspicuously short and straight. In 

 the liver and lungs of an ostrich, packets of short rod-forms are 

 found, while in other parts of the same sections the bacilli attain 

 a very great length. Many of the long, sinuous forms exhibit a 

 peculiar terminal enlargement. There are also short rods with a 

 similar appearance, and free ovoid bodies, singly and in groups, which, 

 from their connection with the bacilli, and their sharply defined 

 outline in the free state, are similar to spores in old cultures. 



Thus, morphological differences are found under different circum- 

 stances, and within limits the morphology of the tubercle bacillus 

 varies with its environment. 



Koch first succeeded in cultivating the bacillus by employing 



