22 Proceedings, 



such substances are composed, and bringing them into the 

 elementary or simple state required for the support of plant- 

 life. Thus it is that some of the ammonia as well as nitrites 

 and nitrates so useful to vegetation are from time to time 

 supplied to the soil. 



We come now to our last subject,' the disease-producing 

 Fungi. Formerly, when epidemic diseases were present, 

 our forefathers said, "they were in the air"; and 

 modern researches have not only proved the truth of this 

 observation, but they have, in part at least, explained it, 

 inasmuch as they have isolated and studied the life-history 

 of some of the organisms on which several infectious diseases 

 depend ; and by this study they have shown that the germs 

 by which they are propagated are exceedingly minute ; that 

 they are so tenacious of life that some of them are capable of 

 inducing disease after being buried twelve years in the earth, 

 while others retain their vitality after being exposed to the 

 beat of boiling water or left in the air till thoroughly dried. 

 Bodies so small and light may of course be easily transported 

 from place to place as constituent parts of the everywhere- 

 abounding air-dust, and carry disease with them. 



The micro-organisms which are recognised as causing 

 disease are arranged in four genera : — 



1. Micrococci, which consist of minute round or oval cells, 

 multiplying by transverse and longitudinal division, and 

 thence presenting themselves as single cells, chains, or 

 smaller or larger groups. Smallpox, cowpox, erysipelas, &c., 

 afford examples ; and pneumonia. 



2. Bacteria. — Small oval or slightly elongated cells. Some 

 species are very fatal to Poultry, Babbits, and Mice. 



3. Bacilli. — Eod-shaped cells, single or connected two 

 together, and often angularly bent at the point of connection. 

 Found in typhoid fever, glanders, scrofulous joints, con- 

 sumption, anthrax, or splenic fever. 



4. Spirilla. — Elongated cells spirally twisted, and often 

 furnished with a flagellum or whip like appendage at the end. 

 Ague and relapsing fever afford examples of this, and Prof. 

 Kay Lankester regards Dr. Koch's Comma Bacillus of cholera 

 as a segment of a spirillum. 



