138 ' H. F. Porraad, 



produce tuberculosis in the rabbit or guinea-pig by means of his ba- 

 cillus, he inoculated indiscriminately into any part of the body, but if 

 he wanted to demonstrate the effects of his parasite in the non -scro- 

 fulous animals, he promptly inoculated into the anterior chamber of 

 the eye, or preferably into the peritoneum. After what has been ex- 

 plained in connection with inflammation in serous membranes , it is 

 evident that these experiments do not prove that the bacillus is the 

 cause of tuberculosis. 



In a future communication I will dwell more upon the experi- 

 mental induction of tuberculosis and on the histology and distribution 

 of tubercular products. Before concluding, however, my present remarks 

 on this point, I would like to refer to some errors into which not well- 

 informed or too exacting experimenters and observers are liable to 

 fall. The chief of these is that some consider nothing as tubercle 

 which does not impress the eye as distinct nodules. Here I desire to 

 recall that miliary aggregations are but secondary products. All pri- 

 mary tubercular products are simple infiltrations of lymphoid cells, 

 like those of any inflammatory process, only that they permanently 

 fill the lymph-spaces, making usually undue pressure upon the blood- 

 vessels, and obliterating the latter. By the unaided eye, or with but 

 low magnifying power, nothing abnormal is noticed, except, perhaps, 

 as in the lungs, some relatively irregular thickenings of the septa or 

 the alveolar walls. In primary tuberculosis there are only in ex- 

 ceptional cases more extensive circumscribed aggregations of lymphoid 

 cells, approaching miliary nodules. Still, this infiltration of cells is 

 sufficient to occlude blood-vessels by pressure, inducing ultimately 

 retrograde changes of the tubercular products, cheesy degeneration 

 of the latter, including the tissue they invade, and, finally, loss of 

 substance. 



It is this absence of distinct miliary nodules which has led to the 

 belief that phthisis might exist without tuberculosis. Giant cells are 

 also no criterion for tuberculous tissues. 



Another source of error lies frequently in the interpretation of 

 experiments. An animal may die too soon, from septicaemia or other 

 acute effects, and in such case it will be alleged that a given inter- 

 ference did not produce tubercular disease; or an animal may not 



