THE COMMUNICABLE DISEASES 513 
sought. Giant cells may be encountered but are not so 
large as in milia. Necrosis occurs but not in an orderly 
manner in relation to cells as in an isolated tubercle. 
Tubercle bacilli are very numerous. 
Types of Bacillary Infection. 
According to experimental and statistical research, 
all the tubercle bacilli of the higher vertebrate classes can 
be infective for any member of these classes. Thus, for 
example, human bacilli have been found in many orders 
of mammalia and in birds. The bovine form has been 
found in swine. The lesson from this is that while the 
special predilection of a variety of the tubercle bacillus 
may be for one kind of animal, it is potentially a vii-us for 
other kinds. Hygienic principles have therefore been laid 
down at the Garden which aim at the protection of all 
specimens from every variety of tubercle bacillus. For 
this reason and because the laboratory has not attempted 
extensive research on bacteriology, few type determina- 
tions have been made and those at hand offer nothing new 
or unusual; they are noted here as a matter of record. 
Bovine bacilli have been judged by their slow growth 
and infectivity for rabbits, human bacilli by the reverse 
of these characters. Avian tubercle bacilli can be culti- 
vated with reasonable ease directly from lesions not 
bearing a mixed bacterial flora, and grow in a yellow, 
moist, even, spreading colonization. In our two attempts 
at infection of guinea-pigs, no success was had, although 
Rabinowitsch and others had no difficulty in so doing ; this 
strain may vary in virulence as do other tubercle bacilli. 
No avian culture was obtained from a mammal, but a 
bovine was found in a parrot and a human in a duck. 
Bovine bacilli were isolated once from a monkey (see 
page 496) and in another case of lymphatic type, bacilli 
of the short heavy blunt shape, supposed to be character- 
istic of this variety of the germ, could be stained. Monkey 
tuberculosis in our experience is usually due to the human 
