i8o MICRO-ORGANISMS AND DISEASE [chap. 



occurs in organic substances left exposed to the dust of air. 

 The best material is bay-infusion. An infusion, cold or 

 hot, of hay is made in a beaker or flask ; the fluid is 

 neutralised, then filtered, covered with a glass plate, and 

 left to stand in a warm place. After a day or two it 

 swarms with bacillus subtilis, which is also called hay- 

 bacillus, since ordinary hay contains multitudes of its 

 spores. For this reason even boiling of the fresh infusion 

 for a few minutes does not sterilise it. 



The bacillus grows well in every fluid that contains the 

 necessary salts and nitrogenous compounds ; thus all kinds 



of/"' ° .^^mm^ 



<^ 



Fig. 53. — From a Culture of Bacillus Subtius (Hay-Bacillus), with 

 Copious Formation of Spores. 



1. Mass of spores embedded in hyaline matrix. 



2. Bacilli. 



3. Single bacilli containing each a spore : the sheath of the bacilli is well seen. 



Magnifying power about 700. 



of broth, all kinds of animal fluids (hydrocele, blood- 

 serum, &c.), gelatine, peptone solution, &c,, are suitable 

 nourishing media. 



The spores of the hay-bacillus are widely distributed in 

 the air, and contaminations by dust are due to its spores. 



Hay-bacillus is an aerobic microbe. 



In gelatine plates it forms liquefying colonies showing 

 characteristic threads radiating from the centre. In stab 

 and streak gelatine cultures it grows rapidly and hquefies 

 the gelatine ; solidified blood-serum is liquefied by the 



