D. B. WARD, M. D. 193 



croscope. In general, however, the bouillon is very in- 

 convenient, as it gives no clue to the manner of growth of 

 the organisms, so we mix with it ten per cent, of gela- 

 tine and make a jelly which is solid at ordinary room 

 temperatures. This is employed in the same way after 

 careful sterilization. Now we note some peculiarities 

 which the beef broth could not show. Some species 

 grow in little colonies so minute that we need a magni- 

 fying glass to see them, an'd these colonies extend all 

 along the track of the needle. Others liquefy the gela- 

 tine, so that in forty-eight hours the whole mass becomes 

 liquid. Some grow most rapidly at the top of the punc- 

 ture in the jelly and some at the bottom furthest away 

 from the air. Indeed, a considerable number will not 

 grow in the presence of air at all. These latter are called 

 anaerobic. Thus we can make another division of the 

 bacteria into aerobic and anaerobic. A few will grow 

 either with or without air, and we call them facultative 

 anaerobics. The tetanus bacillus I have mentioned is a 

 strict anaerobic, and this accounts for the fact that lock- 

 jaw follows usually a punctured wound and not a cut. 

 The puncture closes up and the bacilli which have been 

 carried in, no longer being exposed to the air, grow 

 and produce the disease. It will be found that some 

 species produce colors of various kinds when growing on 

 gelatine or on potatoes; these species are called chromo- 

 genic. One of the most curious of these is a short bacillus 

 — almost a micrococcus — which is called the bacillus pro- 

 dii^iosus. When grown on moist bread or potato it forms 

 red spots or stains which look as if they might be of 

 blood, and this phenomenon has excited great consterna- 

 tion in the days of old, I quote from Prudden's " Story 

 of the Bacteria": "The miracle of the bleeding Host 

 has appeared again and again in the hands of the priestly 

 defenders of the faith as a most potent evidence of divine 

 intervention with the affairs of men. The consecrated 



131 



