150 TUBERCULOSIS 
obtained like results. At present, therefore, we must look upon the 
tubercle bacteria coming from these different species as possessing 
racial or varietal differences which perhaps are the result of different 
life conditions. The investigations which have been made with the 
different forms of this organism found in tuberculosis of fowls and of 
fish have led a few experimenters to believe that they are simply vari- 
eties of the organism first described by Koch. Further inquiries are 
necessary to fully satisfy bacteriologists that all of these forms are 
thus related to the one species. There seems to be no reason for 
doubting that the bovine and human forms are varieties or races 
of the same species. The difference in the conditions of life under 
which they exist in the bodies of men and of cattle is quite 
enough to explain resulting differences in the bacteria. There seems 
to be a tendency for some workers on this subject to consider 
the varietal differences between the human and bovine to be of less 
significance than heretofore thought. Malm found experimen- 
tally that the difference between the bovine and human tubercle 
bacteria is not constant. He states that ‘“‘there are human tubercle 
bacteria that are very virulent for cattle and rabbits. There are also 
of the bovine type varieties that show a weak virulence for cattle, 
rabbits and guinea pigs.’ He believes that no distinction should be 
made between human and bovine varieties. Findlay and Martin 
found that the bovine type was more readily destroyed by daylight 
and drying than the human type. They explain in part by this fact 
the more frequent aerial infection in man. 
Symptoms. The symptoms vary according to the course of the 
disease and the location of the lesions. There isa chronic form, which 
is most common, and an acute form or miliary tuberculosis. 
The symptoms of chronic tuberculosis depend upon the location 
and extent of the lesions. When they are situated deeply and are 
not of great extent, they may not exhibit visible evidence of their 
presence. In such cases, the infected animal may present the picture 
of perfect health and show no disturbance of function. Indeed some 
animals, in which the lesions are both extensive and widely distributed 
and which have never presented noticeable signs of the disease, are 
slaughtered for beef without a suspicion of the presence of tuberculosis 
until they are examined post-mortem. 
Since the lesions of tuberculosis vary so much in different cases, 
it is not possible to give a description of what can be designated the 
characteristic or even the usual symptoms of this disease. In the 
