VI} GENERAL CHARACTERS OF BACTERIA 95 



Finkler, certain water bacteria (bacillus sulcatus) ; (b) the ma- 

 jority grow well not only at low temperatures but grow best at 

 temperatures above 22° C. ; and a still further gronp (c) com- 

 prises bacteria which do not grow at all or only very feebly 

 at temperatures below 22° C. To the latter class belong the 

 pneumococcusof Fraenkel, the bacillus tuberculosis. Amongst 

 groups l> and c the optimum temperatures lie between 28 

 and 38° C. Higher temperatures than 38" C. have on these 

 two groups a retarding influence, which is feeble one or two 

 degrees above this figure, but becomes in many cases pro- 

 nounced above 40° C. But this is not the case with all, 

 since, for instance, bacillus anthracis and bacillus tuber- 

 culosis at 42 '5 or even 43° C. show still copious growth. 



Miquel described one species of spore-forming bacillus, 

 which, strange to say, has its natural habitat in soil, the 

 bacillus termophilus ; it grows well at temperatures at 

 which other bacteria are prevented from growing, injured and 

 even killed; this bacillus termophilus grows well at 65° C, 

 and forms spores at 70-75° C. 



In all cases of bacteria that do not form spores — and the 

 majority of species are of this kind — an exposure to a tem- 

 perature of 60-70° C. for ten to thirty minutes devitalises 

 them, but there are slight differences to be noticed — e.g. 

 whereas the bacillus coli is not killed by exposure for five 

 minutes to a temperature of 62° C., the typhoid bacillus is 

 killed under these conditions. All non-sporing bacteria 

 (also those that are capable of forming spores but do not 

 contain them, or had not formed them yet in particular 

 cultures) are invariably killed when exposed for five to ten 

 minutes to a temperature of 70° C. 



Spores of bacilli are not killed even by an exposure to 

 98° C. for a minute or two ; there exist differences in this, 

 for while the spores of bacillus anthracis are killed at 100° C. 



