126 THE GERM THEORY OF DISEASE. 



ALKALOIDS. 



There is, perhaps, no other one set of organic compounds 

 that have puzzled chemists more than those given in this 

 table, or that have been and still continue to be of more in- 

 terest to the scientific world. The table, as it stands, is only 

 intended to give an outline view of these organic matters as a 

 class, by setting before you fairly chosen specimens from the 

 different forms of life. It is not intended to be in any wise 

 exhaustive, but simply a comparison of these products. The 

 similarity of their chemical construction will be apparent at a 

 glance, and yet they differ greatly in their toxic properties. 

 Some, as strychnine, are violent poisons to the animal king- 

 dom. While others, as some of the acids, are mild irritants. 

 Most of those from the vegetable world are useful as medi- 

 cines, while many are highly prized as condiments. The 

 members of the acid series vary from the alkaloids in that 

 they contain no nitrogen, and they also vary as markedly in 

 their toxic properties. Their close similarity to the alcohols 

 will be noticed. It will also be noticed that some of the 

 waste products of higher plants are the same as those of lower 

 organisms. This, perhaps, would not be expected at first 

 glance; yet when we come to consider that all are plants, we 

 should expect a similarity. There is, perhaps, an important 

 difference to be observed here. The alkaloids of the higher 

 plants, from the nature of their mode of excretion, are thrown 

 out of physiological activity, by being combined with the veg- 

 etable acids, mostly in the form of insoluble salts, and thus 

 laid away in the " fixed material " of the plant. On the other 

 hand, the animal alkaloids, urea, uric acid, etc., are eliminated 

 in a soluble condition. In case of the micro-organisms, the 

 waste products are very generally eliminated in a soluble 

 condition also. There seem to be some exceptions to this 



