THE BIOLOGY OF BACTERIA 19 



to its highest vegetative growth, and so it endeavours to 

 perpetuate its species. Most authorities are probably of the 

 latter opinion, though there is not a little evidence for the 

 former. Exactly what conditions are favourable to sporula- 

 tion is not known. Nutriment has probably an intimate 

 effect upon it. The temperature must not be below 16 C., 

 nor much above 40 C. Oxygen, as we have seen, is favour- 

 able, if not necessary, to many species, which will in cultiva- 

 tion in broth rise to the surface and lodge in the pellicle to 

 form their seeds. Moisture, too, is considered a necessity. 



The position and size of the spore are of considerable use in 

 differential diagnosis. The terminal spore of Bacillus tetani 

 is well known. It is rarely seen at both ends of the bacillus, 

 and hence when poised only at one end causes the " drum- 

 stick " appearance. In the bacillus of Quarter Evil the 

 spore is generally towards one end of the rod rather than 

 in the middle ; in Malignant CEdema the bacillus in the 

 blood grows out into long threads, and when such a thread 

 sporulates the spore is also near one end. The latter further 

 illustrates the fact that in some species the spore is of 

 greater diameter than the mother cell, and hence dilates 

 the bacillary capsule. The spores of anthrax are typical 

 oval endospores. When free in the field of the microscope, 

 spores must be distinguished from fat cells, micrococci, 

 starch cells, some kinds of ova, yeast cells, and other like 

 objects. Spores are detected frequently by their resistance 

 to ordinary stains and the necessity of colouring them by 

 special staining methods. When, however, a spore has 

 taken on the desired colour, it retains it with tenacity. In 

 addition to their shape, size, thickened capsule, and staining 

 characteristics, spores also resist desiccation and heat in a 

 much higher degree than bacilli not bearing spores. Roux 

 and some other eminent bacteriologists suggest that bacteria 

 should be classified according to their method of spore 

 formation. 



