114 MANUAL OF BACTERIOLOGY. 



that do not. There should be chromogenic forms , and species 

 that ferment dextrose, and that produce indol,— such species 

 as some of the sarcinas, the bacillus coli communis, the hay 

 bacillus, the potato bacillus, bacillus prodigiosus, a bacillus 

 fluorescens and spirillum rubrum. It is well, when possible, 

 to obtain material directly from nature rather than from 

 laboratory cultures. This may readily be done in the case of 

 the hay bacillus and the potato bacillus. Fecal matter may be 

 spread on gelatin plates and the bacillus coli communis ob- 

 tained in pure culture. Fluorescing bacilli are very common 

 in water. Large spirilla are often found in swamp water. 

 Some organisms like spirillum rubrum can only be had from 

 laboratory cultures. An instructive experiment which any- 

 one may carry out is to boil a potato thoroughly, and cut it 

 into slices, placing these on moist filter-paper on glass plates, 

 or on saucers, and after exposing them to the air for half an 

 hour or more to cover them each with an inverted tumbler. 

 Some of the slices prepared in this way should be put in the 

 incubator, others left at room temperature. In a shorter or 

 longer time there usually develops a great variety of isolated 

 colonies from the bacteria that have fallen on the slices of potato. 

 The growth of some aerobic organism, like the potato bacillus, 

 may be tested under a cover-glass (see Fig. 29). The pyogenic 

 bacteria, which can easily be isolated from pus, may be studied 

 in this connection with great advantage. The staphylococcus 

 pyogenes aureus and the streptococcus pyogenes should on no 

 account be omitted. The diplococcus of pneumonia can most 

 readily be obtained from a mouse or a rabbit which has died 

 with pneumococcus infection. Such an animal can best be 

 infected by subcutaneous inoculation, using some of the rusty 

 sputum of a case of lobar pneumonia. The cultivation of the 

 pneumococcus will be found to present difficulties in classes 

 containing large numbers of students. 



Representative forms of moulds and yeasts should be studied 



