In this paper the pathological and the bacteriological findings in ten instances of naturally acquired tuberculosis in ten different species of animals are recorded. The tubercle bacilli obtained in culture from five species (bat, bear, bison, hedgehog and mink), all cases of fatal tuberculosis, were of the bovine type. The bacilli from a case of localised glandular tuberculosis in a goat and one of tuberculosis of the pancreas in a kangaroo were of the avian type. The bacilli from a case of generalised retrogressive tuberculosis in a horse, of minimal thoracic tuberculosis in a calf and cutaneous and glandular tuberculosis in a parrot were of the human type. These results amplify the evidence already published which shows that each of the three types of tubercle bacilli (bovine, human and avian) is able to cause natural tuberculosis in many different species of animals other than that which is its normal habitat.

The bovine bacillus which is transmitted to animals almost exclusively by tuberculous bovines is responsible for the greater part, especially the generalised and fatal forms, of the tuberculous disease occurring naturally in farm and domestic mammals and for a not inconsiderable amount of tuberculosis in human beings.

The avian bacillus whose natural host is the domestic fowl can infect casually many species of mammals, namely the pig, the ox, the sheep, the goat, the horse, the guinea-pig and the rabbit and in Zoological Gardens several marsupial species. Instances of its transmission to the different species of farm mammals are rare, except in the case of the pig, and the disease produced is usually limited and confined to the glands adjacent to the points of entry of the bacilli. This type of bacillus may however cause severe generalised and fatal disease in the pig, sheep, rabbit and marsupials.

The human bacillus has a narrower range of pathogenicity than either the bovine or the avian bacillus. This type can infect the pig, the calf and the horse, but does not produce progressive tuberculosis in these species. It causes cutaneous tuberculosis in parrots and is one cause of tuberculosis in the dog and in various species of animals kept in captivity, namely the guinea-pig, monkey, gnu, antelope, peccary, etc., in which species infection is followed by generalisation and progression of the disease.

The evidence accumulated regarding the susceptibility of various species of animals to the three types of tubercle bacilli under farm and domestic conditions and in captivity may be summed up as follows.

All three types of bacilli can infect the ox, pig, horse, guinea-pig and rabbit.

Two types of bacilli have been found in the following species; viz. bovine and avian in the sheep, the goat and Australian marsupials; bovine and human in the domestic dog and in the ape, monkey and Ungulata in captivity; human and avian in the parrot.

Only one type of bacillus has so far been obtained from domestic fowls (the avian), the domestic cat, hedgehog, mink and ferret (the bovine) and members of several species in captivity.