34 Lectures on Bacteria. [^ iv. 



lacticus is at first most active at a low temperature, and turns the 

 milk sour by the formation of lactic acid ; it is killed by boiling, 

 but the spores of Bacillus Amylobacter, the Bacillus of butyric 

 acid, which is also present in the milk retain their vitality, and 

 this Bacillus causes the decompositions in boiled milk which 

 give it a bitter taste. 



Another instance of the same kind is the statement ema- 

 nating from Nageli's laboratory, that the hay-bacillus, Bacillus 

 subtilis, is identical with Bacillus Anthracis, the Bacillus of 

 anthrax. The two species are very like each other, and Buch- 

 ner's observations certainly contain some true remarks about 

 them, which will be discussed in Lecture XII. But the most 

 striking characteristic of B. subtilis is the often-described ger- 

 mination of its spores, the growing out of the germ-cell from 

 the transverse fissure of the spore-membrane at right angles tO 

 the longitudinal axis of the spore. The Bacillus of anthrax 

 does not exhibit this phenomenon, as Buchner himself tells us. 

 But due regard has nowhere been paid to these differences, so 

 that it is still doubtful whether Buchner has examined B. subtilis 

 at all. In this case too the morphological statement is without 

 certain foundation and justification. 



The increased attention bestowed by observers on this subject, 

 beginning with the wheat-plant and going down through various 

 larger forms of the lower plants to Bacteria, has done away 

 one after another with the erroneous notions indicated, and led 

 to the general adoption of the view above explained, that ques- 

 tions of species are essentially ahke throughout the series of 

 organisms. In the case of the Bacteria much still remains to 

 be done ; our knowledge of these is yet only in its infancy. 



I say that increased attention is leading to this result. I 

 should wish at the same time to point out once more the con- 

 ditions which have been and which are of the first importance. 

 As might be expected, the aids to investigation, apparatus, tech- 

 nical methods, reagents, &c., have been improved. To deter- 

 mine the questions which we are at present considering, minute 



