DOCTRINE OF A CONTAGIUM VIVUM. 37 



As regards the defensive action of the leucocytes, I need only 

 give a quotation from Bland Sutton (p. 127) : — 



" If we summarise the story of inflammation, it should be 

 likened to a battle. The leucocytes are the defending army, their 

 roads and lines of communication the blood-vessels. Every 

 composite organism maintains a certain proportion of leucocytes 

 as representing its standing army. When the body is invaded by 

 bacilli, bacteria, micrococci, chemical, or other irritants, informa- 

 tion of the aggression is telegraphed by means of the vaso motor 

 nerves^ and leucocytes rush to the attack. Reinforcements and 

 recruits are quickly formed to increase the standing army — 

 som-etimes twenty, thirty, or forty times the normal standard. In 

 the conflict cells die, and often are eaten by their companions. 

 Frequently the slaughter is so great that the tissue becomes 

 burdened by the dead bodies of the soldiers in the form of pus, 

 the activity of the cell being testified by the fact that its pro- 

 toplasm often contains baciUi, etc., in various stages of destruction. 

 Those dead cells, like the corpses of soldiers who fall in battle, 

 later become hurtful to the organism they in their lifetime were 

 anxious to protect from harm, for they are fertile sources of 

 septicaemia and pyaemia." 



The most effectual method of introduction of a bacterial 

 poison is by inoculation. This in the lower animals is a certain 

 method, and there have been a few instances recorded of the 

 accidental inoculation of the tubercle bacillus into the human 

 subject ; the skin, when intact, is a very effectual barrier, and even 

 when ulcerated is rarely the source of blood contamination. 



We are now able to realise how it is that there are varying de- 

 grees of contagion, and how it has come to pass that such a disease 

 as tuberculosis is not yet classed amongst contagious diseases. We 

 have seen that the spores have a difficulty in finding their way 

 through the opposing barriers, and so inoculating the circulat- 

 ing fluid. These difficulties will vary with the individual germ, 

 and account for the varying degrees and limitations of the conta- 

 gious quality amongst the different members of the group of 

 diseases classed as contagious. 



It is difficult to define accurately or to limit the powers of 

 resistance of the body to contagion. As is well known, no hard 



