SYSTEMATIC STUDY OF SPECIES OF BACTERIA. I03 



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 theseon moist filter paper on glass plates, 

 or on saucers, and after exposing them to the air for a 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 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 pneu- 

 mococcus 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 

 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 maybe isolated in pure culture from gelatin plates. 

 Bacteriological examinations also should be made of air, soil, 

 water and milk. With such simple means, many of the important 

 properties of bacteria may be demonstrated. It is most im- 

 portant that medical students should convince themselves by 

 experiment of the extent to which bacteria are disseminated in 

 our environments. The bearings of such observations on the 

 practice of surgery and hygiene are obvious. 



