250 MISSOURI AGRICULTURAL REPORT. 



very low form of life, being unicellular. Most of our infectious diseases 

 are caused by very low forms classed in the vegetable kingdom. ]Most of 

 them are very small, so small that you might lay 25,000 of them side by 

 side and thus cover only one inch of space: Some are even smaller than 

 this. Tliey are of various shapes and sizes, some round, others oblong, 

 rod shaped, corkscrew shaped, etc. Almost eight hundred different forms 

 of bacteria have been described. Many would also cause disease to 

 plants and animals. 



Bacteria are extremely small one-celled vegetable organisms, con- 

 taining no chlorophyll and multiplying by division. For a long time it 

 was not known just why bacteria produced disease. Now in nearly all 

 cases we know that disease is caused by a specific poison which the germ 

 produces during its growth and disintegration. A living cell secretes and 

 excretes certain substances. When the cell is destroyed certain other 

 substances may be liberated. Now if these substances happen to be pois- 

 onous or harmful to a human body and should gain admission to a human 

 body a disease would arise in this body. Suppose the typhoid germ 

 should gain admission to your body, and should multiply in your body, 

 and during its multiplication these little germs should secrete or excrete 

 a poison harmful to your body you would then suffer from typhoid fever. 

 You would not develop typhoid fever until sufficient poison was produced 

 to distinctly interfere with your vital processes. Thus the dose of poison 

 which would be harmful to you might not injure me and I go unharmed. 

 Now we know these things to be facts. We know that these diiferent 

 forms of disease germs secrete distinct and different forms of poison, 

 for we can isolate these poisons and demonstrate them on animals. In 

 fact we can measure them out in doses just like you would strychnine or 

 any other powerful poison. However we connot get them entirely pure. 



The poisons from a particular disease germ will produce the same dis- 

 ease if the poisons are given in a sufficient dose, that is, produced by the 

 living germ itself. There is this diiference, however, if one use only the 

 poison and not the living germ, of course the disease will not spread, for 

 the poison itself cannot grow any more than strychnine can grow of itself. 

 Thus you see that in most infectious diseases in order for one to recover 

 from such a disease he must be able to resist the poisons produced. The 

 mere presence of the very small bacteria would do no great harm in them- 

 selves, but it is the poisons which they produce. There are some apparent 

 exceptions but we wjll not discuss that here. 



Some of these poisons are fatal in extremely small doses, even in im- 

 pure form for we have not been able to purify them. Thus Brieger and 

 Cohn found that 0.000,000,05 grains of impure tetanus or lockjaw poison 

 was sufficient to kill a mouse 15 grams in weight. Expressed -in terms so 



