TEXT-BOOK OF BACTERIOLOGY. 191 



nary circumstances, and only under special conditions for example, 

 when the power of resistance in the tissues is diminished penetrate 

 into the latter, multiply in the blood, and so take a pathogenic 

 character, which is clearly perceptible also in experiments per- 

 formed on animals. 



BACILLUS SPINOSUS. 



It is desirable that we should consider a certain harmless, non- 

 pathogenic member of the important class of anaerobic bacteria, by 

 the examination of which we may be enabled to study the peculiar- 

 ities of these remarkable micro-organisms. We refer to the Bacil- 

 lus spinosus of Liideritz, which displays a very high degree of sen- 

 sitiveness to the effects of atmospheric oxygen. 



It may be remembered that the anaerobic bacteria are far 

 more widely diffused in nature than one might at first suppose, and 

 that the anaerobic micro-organisms are almost always to be found 

 in water, in putrefying liquids, and in the upper layers of earth, 

 especially garden earth. It is from the latter source too that we 

 obtain the Bacillus spinosus. Put a little dry earth into a pouch in 

 the abdominal wall of a Guinea-pig, and after about two days the 

 animal generally dies from the effects of a pathogenic, anaerobic 

 species which will be further considered in its proper place. This 

 species, however, is never found alone. The material used for inocu- 

 lation always contains the germs of several kinds of anaerobic 

 bacteria, which multiply in the animal's body and adopt a parasitic 

 way of life, but which, as far as we have yet been able to perceive, do 

 not seem able themselves to play a pathogenic part. 



Among these is the spinosus. It is a very large, moderately- 

 thick rod-cell, with brisk spontaneous movement, which generally 

 proceeds quickly to sporulation. The spore-formation takes place 

 in the middle of the cell, and the spore-bearing bacillus often bulges 

 somewhat at the place where the spore lies, producing forms which 

 remind us of those of the clostridia. The cells take the anilin stains 

 well; the spores may be brought into prominence by special stain- 

 ing in the usual way. 



Our artificial food media receive, as we know, for the culture of 

 anaerobic bacteria, an addition of \<f> or 2$ of grape-sugar, or some 

 other reducing agent. If the spinosus be put into gelatin thus 

 prepared, the inoculating material distributed in a thick layer, and 

 the colonies allowed to develop, we will find that at ordinary room- 

 temperature the growth will become clearly visible in two or three 

 days. First in the original tube, later in the dilutions, small white 

 dots appear, which quickly increase in size and liqufey the medium 



