XVlll 



destroys the protecting cells which then become the prey of the 

 invading bacilli ; but the effect produced by small quantities of 

 this potaine is to stimulate the action of the cells, at the same 

 time causing a dilatation of the vessels, by which means a larger 

 amount of food material is brought up for the nutrition of the 

 cells, while the exhausted matter is more readily carried off ; and 

 it was with the idea of assisting these cells to resist the encroach- 

 ments of the bacilli that he adopted the method of treatment 

 which for a time excited hopes that unfortunately have not been 

 fully realised ; his inoculating material is not the attenuated 

 bacillus tuberculosis, but what he himself describes as "a 

 glycerine extract of pure cultivations of tubercle bacilli," and, 

 although it has failed to produce the beneficial results that were 

 anticipated, there seems no reason for doubting the existence of 

 the principle of which his tuberculin was an attempted artificial 

 adaptation. 



As a partial explanation, therefore, of the comparative im- 

 munity from diseases which would carry off tens of thousands of 

 victims if the conditions were always favourable to their attacks, 

 we have — first, the power of the tissue cells in healthy persons to 

 destroy and in others to resist the attacking bacilli ; we have the 

 invigorating effect of the toxic products of the bacilli upon the 

 tissue cells when these find their way into the body ; and we 

 have also the insuperable difficulty to the anccrohic nn/anisins of 

 pursuing their course when the oxygen of the air reaches them 

 directly from without, or indirectly from within through the 

 agency of the tissue cells ; and to t/w ccrohic ori/anisms when the 

 supply of oxygen they require is curtailed by the demand made 

 upon it by the tissue cells or by other and innocuous cerobic 

 bacilli. 



And now let us remember that, although the old theory of 

 abiogenesis, or spontaneous generation, has been completely 

 demolished by the discoveries of Pasteur and others who have 

 followed in his footsteps, and that it is now allowed that every 

 disease is attributable to the agency of organisms in the absence 

 of Avhich it could not have originated, the number of pathogenic 

 bacteria is small compared with those which are harmless. The 

 air we breathe, the water we drink, the food we consume, — 

 everything, in fact, with which we are continually brought into 



