no MICRO-ORGANISMS AND DISEASE. [CHAP. 



thickness. They do not stain in ordinary dyes, and hence 

 form a great contrast to the bacilli. 



This bacillus is very common and widely distributed ; it 

 occurs in almost every organic substance rich in nitrogenous 

 compounds which is left exposed to the air to decompose. 

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

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



sn'i oj 



FIG. 46. GERMINATION OF SPORES INTO BACILLI. 



a. Spores of a small kind. 



b. Spores of a larger kind of bacillus subtilis. 



Magnifying power about 700. 



The bacillus grows well in every fluid that contains the 

 necessary salts and nitrogenous compounds ; thus all kinds 

 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 most contaminations by air are due to its 

 spores. 



(b) Bacillus ulna. By this name Cohn * designates certain 

 species of bacilli, stiffer and thicker than those of bacillus 

 subtilis. The individual elements are about o'oi mm. long, 

 1 Loc. cit. p. 177. 



