INFECTIOUS DISEASES AND MICROBES, ETC. 245 



Tuberculosis, or that form of the disease known 

 as phthisis (consumption), runs through certain 

 families. There are two theories which account for 

 the inheritance of phthisis (a) that the tissues of 

 children born of phthisical parents are especially 

 favourable to nourish the tubercle bacilli; i.e. the 

 tissues form a fertile soil for the subsequent growth 

 of the microbes; (b) that the tubercle bacilli are 

 actually contained in the ovum or among the sper- 

 matozoa, and so become a constituent part of the 

 embryo and foetus which develops within the 

 uterus. Baumgarten records the fact that he has 

 observed the tubercle bacilli in the ovum of the 

 rabbit, and many observers have frequently seen 

 the bacilli mingled with active spermatozoa. Pro- 

 fessor Johne, of Dresden, discovered numerous 

 tubercles in the lungs of a foetal calf of seven 

 months intra-uterine growth. This proves that if 

 the ovum had not been inoculated, it received the 

 virus (i.e. the tubercle bacilli) through the placenta, 

 which amounts practically to the same thing. 

 Similar intra-uterine inoculation has been shown 

 to be more than probable in the human being ; and 

 Professor Burdon Sanderson 1 believes that many 

 cases of phthisis are congenital, i.e. dependent on 

 causes which have operated before birth. 



Besides being hereditary, tuberculosis is also 

 infectious, i.e. the disease is capable of being trans- 

 mitted by direct or indirect infection from one host 

 to another. 



There are four modes in which the tubercle 



1 Report of International Congress of Hygiene, 1891. 



