532 CLINICAL VETERINARY MEDICINE AND SURGERY. 



though at first limited to the centre of the tubercle, and producing the 

 appearance of a clear centre surrounded by special epithelioid cells, 

 afterwards extends to the whole of the new growth and tends to en- 

 cystment. 



The histological appearances of tuberculosis of the liver in the 

 fowl and in the pheasant so greatly differ that at first sight the micro- 

 organisms producing the lesions might be regarded as of different 

 species. This interpretation, however, would be erroneous. 



We have inoculated from the pheasant to the fowl, and in the 

 liver of the latter have found histological lesions identical with those 

 of spontaneous fowl tuberculosis. 



Although the production of tubercles, both in the fowl and in the 

 pheasant, is due to the same bacillus, the development of these growths 

 is none the less affected by peculiarities of the host. It is the story 

 once more of the grain and the soil. Not only do the hepatic tubercles 

 in the fowl and pheasant differ from hepatic tubercles in mammals, but 

 they vary to a marked extent between themselves, although developed 

 in such nearly related species. We cannot lay too much stress on this 

 fact, which throws so prominently into relief the pathological peculiari- 

 ties of animals, and which shows how dangerous it is to indulge in 

 general conclusions drawn from experiments on a single species. 



IV.— EXPERIMENTAL STUDY. 



Only one method existed of determining the nature of avian 

 tuberculosis, viz. the experimental. Only after having shown how the 

 virus of avian tuberculosis behaves in mammals, and how that of 

 mammals behaves in birds, could we even attack the continually recur- 

 ring problem of the unicity of tuberculosis in various species of animals. 

 We may therefore divide this chapter into two parts, and we shall 

 commence b}' giving the particulars of experiments made with avian 

 tuberculosis. 



Part I. — Inocidation Experiments with Tuberculosis of the GallinacecB. 



To study the effects of the avian virus we directly inoculated from 

 lesions developed in the Gallinacese and utilised in our experiments a 

 considerable number of birds drawn from different localities, a fact which 

 may be regarded as giving a certain general character to our results, 

 and also explaining some apparently contradictory results which we 

 have observed. 



We obtained our virulent material from eleven subjects — eight 

 fowls, two pheasants, and one guinea-fowl — sent us b)' different owners 

 and breeders. In all these animals post-nwrtcin examination showed 



