THE LIVING ORGANISM 205 



sites of growth of different micro-organisms 

 in the body; for the chemical constitution 

 of one kind of cell, such as a cell in the intestine 

 say, suits one organism, while another finds 

 its best pabulum in the lung, another in 

 muscle, and another in the cavity of a joint. 

 By means of the chemical sympathy above 

 mentioned, while one site may best suit the 

 growth of an organism, quite another site 

 and type of cell may be most adapted to 

 react with its poison, or toxin, so the obvious 

 and dangerous results of the disease may 

 appear at points remote from the invading 

 army. Thus, the organism responsible for 

 the production of diphtheria, for example, 

 grows in a restricted area of the tonsils 

 and throat, small compared with the bulk 

 of the body. Apart from occasional diffi- 

 culties of a mechanical nature connected 

 with respiration, the local effects are not 

 dangerous. But the minute organisms produce 

 a soluble chemical substance, the diphtheria 

 toxin, which is of the same order of deadliness 

 as snake venom. This is discharged into 

 the blood stream, and is absorbed chiefly 

 by two types of body-cells, on account of the 

 above-mentioned chemical adaptation of its 

 molecule to their particular colloids. These 

 two tissues happen to be master-tissues of 



