APPENDIX. 237 



test-tube, the powder added, and, in the usual way, dis- 

 tributed throughout the medium, which is then poured 

 out upon a glass plate. Just in the same way the 

 dust which settles from the air in houses and hospitals, 

 or food substances in powder, may be distributed over 

 nutrient gelatine, and the micro-organisms which develop 

 studied, both as to their morphological and biological 

 characteristics. 



APPENDIX D. 



EXAMINATION OF WATER. 



As in the case of air, so, too, in that of water a knowledge 

 of the micro-organisms which may be present is not only 

 of interest to the microbiologist, but of the greatest 

 importance in practical hygiene. Common putrefactive 

 bacteria and vibrios may not be hurtful in themselves, but 

 they indicate the probability of the presence of organic 

 matter in some of which there may be danger.* 



The Microzyme Test, which was introduced for 

 their detection, consisted in adding three or four drops of 

 the sample of water to I or 2 ccm. of Pasteur's fluid, 

 the nourishing fluid having been previously boiled in a 

 sterilised test-tube. If the microzymes or their germs 

 existed in the water, the liquid in a few days became 

 milky from the presence of countless bacteria. This 

 test is of no real value, for it does little more than indi- 

 cate that bacteria were present, which we may accept as 

 being present in ice and all ordinary water. On the other 

 hand, the bacteriological test of Professor Koch is a most 

 valuable addition to the usual methods of water-analysis. 

 It enables us not only to detect the presence of bacteria, 

 but to ascertain approximately their number, and to study 

 very minutely their morphological and biological charac- 



* Parkes, Manual of Practical Hygiene. 1883. 



