114 MANUAL OF BACTERIOLOGY. 



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 com- 

 munis obtained 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. 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 con- 

 nection 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 in- 

 fected 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 at the same time. Moulds are easily obtained by 

 exposing some nutrient substance to the air, covering it, 

 and allowing cultures to develop ; yeasts will probably grow 

 also. Ordinary brewer's yeast may be isolated in pure cul- 

 ture from gelatin plates. Bacteriological examinations also 

 should be made of air, soil, water and milk. With such 

 simple means, all the important properties of bacteria may 

 be demonstrated. 



Experiments in sterilization and disinfection as described 

 in Chapter VIII. , Part II. , may be performed with the bac- 

 teria mentioned, which present every variety of resisting 

 power up to the almost incredible toughness of the spores of 

 the hay and potato bacilli. The efficiency of the methods 



