804 



METHODS OF INVESTIGATING BACTERIA. 



with smaller and larger doses, and the organisms must 

 be introduced either by superficial inoculation, or by in- 

 jection into the subcutaneous tissue, or by direct injec- 

 tion into the blood stream. If the animals become ill 

 or die similar attempts at cultivation and inoculation 

 must be made with their blood or organs, and the 

 identity of the organisms inoculated with those found 

 must be ascertained. All these experiments must be 

 frequently repeated. Lastly, we must make experi- 

 ments as to the conditions of death of the organisms, and 

 more especially as to the loss of their pathogenic pro- 

 perties, and we must ascertain what external conditions 

 and what disinfecting means can most readily cause 

 their destruction (see p. 653). 



Examination 

 of air. 



Miguel's 

 method. 



3. Bacteriological Investigation of Air, Water, and 

 Soil. 



a. Air. Attempts were formerly made to ascertain 

 the number, species, and vitality of the organisms pre- 

 sent in the air by fixing the 

 germs on sticky surfaces, and 

 by subsequent microscopical 

 examination. These attempts 

 were, however, failures, but in 

 recent times fresh methods have 

 been devised, the essential aim 

 of which is to obtain a develop- 

 ment of the individual germs, 

 and then to count the colonies. 

 Miquel employed for this pur- 

 pose a fluid nutrient substra- 

 tum, a broth prepared some- 

 what after the method described 

 on p. 792 : this material was in- 



Fig. 143. Miquel's ap- 

 paratus for the investi- troduced into a large number oi 



small glass vessels of the form 



shown in fig. 143. These sterilised vessels were fixed in a 

 stand, the end/ was connected with an aspirator, and the 



