54 



lower animals, as rabV)its and guinea jHgs, the disease may be 

 transmitted, as was shown by the experiments of Berheimand 

 others, and laid before the second Congress on Tuberculosis 

 in Paris, 1891. It has seldom been found in calves, and 

 rarely in new born infants. 



While tuberculosis in some forms may be transmitted 

 directly from parent to child, there is a very strong consensus 

 of opinion that the form which affects the lungs is never so 

 transmitted. But even in these cases, those who believe 

 strongly in heredity will tell you that the germ has been in 

 the system in a latent condition, while the tissues have been 

 active, only asserting itself when the tissues have become 

 more matured. But is the prevalence of consumption at this 

 time not more likely to be due to the result of taking one's 

 place in the world and being exposed to additional risks in 

 the workroom, the office, etc. i^ It may then be taken for 

 granted that "ConsumjDtion" is not hereditary, but only a pre- 

 disposition ; what that predisposition is we cannot yet say. 

 Dr. Springthorpe, who has devoted a very large amount of 

 study to this subject, speaking at the Medical Congress in 

 Dunedin this year, defined it as " a bacterio-chemical question, 

 affecting the strength of cells and serum in the struggle for 

 existence with the invading microbe." 



One thing seems certain, without this constitutional want 

 of resistance the microbe is unable to invade and thrive in 

 the tissues. This inherited tendency may be intensified, or 

 it may be removed, but it will not, however intense in itself, 

 cause the disease ; the germ must be present. In the re- 

 moving of this tendency lies the opportunity of preventive 

 medicine, for there is usually ample time to correct this in- 

 herited t-endency by careful attention to developmental 

 requirements before " consumption " sets in. 



Admitting then that heredity stands in rare cases as a 

 channel of infection in some forms of tuberculosis, but in 

 the majority of instances as only a predisposing cause, we 

 now pass on to consider other circumstances which act as 

 purely predisposing causes. 



Predisposing Causes. — Certain conditions such as damp- 

 ness of soil, impurity of atmosphere, are important factors in 

 the aetiology of tuberculosis. 



1. Dampness op Soil. — Dr. Buchanan and Sir John Simon 

 have long since proved that " the drying of soil which has in 

 most cases accompanied the laying of main sewers in the 

 improved towns has led to the diminution more or less con- 

 siderable of phthisis. They go on to quote certain cities 

 where such improvements have been made and with what 

 effect on the mortality of phthisis. They take 13 cities in 



