TUBERCULOSIS 145 



suspected to be affected with tuberculosis. The other 

 two samples, which were more virulent, came from dairies 

 where there was more than one suspected cow, and where 

 the udders of some of the animals were visibly tubercu- 

 lous. 



As has already been stated, the tubercle bacillus retains 

 its virulence for a considerable period of time on desiccation. 

 Messrs. Cadeac and Malet produced tuberculosis in guinea- 

 pigs by injecting material from the lung of a tuberculous 

 cow which had been kept in the form of a dried powder for 

 five months, but they found in this particular case that at a 

 later date the virulence was lost. 



The ability of the bacillus of tuberculosis to form spores, 

 and the obstinacy with which they retain their vitality in 

 dried sputum, amply compensates for its inability to grow 

 outside the body (except on special media), and makes it 

 the most fatal and prevalent disease in these Northern 

 climates. In observations and experiments made inde- 

 pendently in Germany, Italy, and France by Kossel, 

 Brouardel, and Picini, the disease was found latent, post- 

 mortem, in 40 to 60 per cent, of persons who had dis- 

 closed no symptoms during life. 



Pathogenesis. — Localised tubercular affections may occur 



in almost every part of the body. The bacilli or spores, 



having been inspired and entering into the circulation, 



invade the weakest part. A local traumatic injury may 



thus determine the onset of the disease in that portion of 



the body affected. Many diseases predispose to phthisis, 



as, for example, whooping-cough, pneumonia, diphtheria, 



scarlet fever, typhoid, syphilis, etc. The bacillus has 



occasionally been found in the foetus, but not often enough 



to afford evidence that hereditary transmission is common. 



When we consider, however, that, as above stated, quite 



50 per cent, of patients have a phthisical history— that is 



10 



