232 Philosophy of Botany. 



the same method investigates the scientist the occult laws of 

 life by comparison of the simplest functions of the cells. Thus 

 succeeded the genial Virchow to construct a system of pathol- 

 ogy upon the presence of diseased cells. 



A very great interest attaches to the recent investigations, 

 about fungi. Problems of surpassing importance, the solu- 

 tion of which the whole civilized world is eagerly awaiting, 

 are thereby involved. Rust, blight, and mildews have from 

 time immemorial ruined the crops. During the last quarter 

 of a century nearly all cultivated plants have been visited by 

 epidemics, which commenced locally, here and there, and were 

 unheeded, and then spread themselves at once over whole 

 countries, leaving failure of crops and famine in their train. A 

 terrible plague has been the potato disease since 1845, and the 

 diseases of the grapevines since 1848. Even the insects, from 

 the common fly to the silkworm and the forest-devouring 

 caterpillars, are infected by plagues. The pebrine, or silk- 

 worm disease, worked great injury to the silk industry and 

 threatened thereby to seriously affect the wealth of a nation. 



We now know that all these epidemics are caused by micro- 

 scopic fungi, and spread by the dispersion of their spores, 

 which communicate from plant to plant, and from insect to in- 

 sect, the germ of a fatal disease. 



After ' these facts had been satisfactorily established the 

 question necessarily came up, whether or not these insidious 

 plagues which, traveling from land to land, to remain here 

 and there for a while, and then to disappear, to return again 

 probably after a short interval, such as cholera, typhus, small- 

 pox, scarlatina, and epidemic diseases of domestic animals, 

 were also brought about by the presence of microscopic fungi ? 



Up to this day we have actually learned that such is the case 

 in diphtheria, scarlatina. Oriental plague, cholera, intermit- 

 tent and relapsing fever, yellow fever, and tuberculosis, and 

 in hospital gangrene, smallpox, septicaemia, and even some 

 other non-epidemic diseases. 



Knowing now the nature .of the invisible enemy, we may 

 hope to devise rneans to keep off the enemy, or to avert its 

 ravages. 



In former times there had been an intimate connection be- 



