MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 7 



in which the organism is able to develop itself undisturbed, 

 apart from the question whether foreign individuals or species 

 are present in the same preparation. In the latter case, on 

 the contrary, an absolutely pure culture is required. 



Cultures of the first-mentioned kind may in certain cases 

 be of use in affording information when the case previously 

 mentioned occurs : a nutritive solution in which deposits 

 of various kinds have assumed a more or less deceptive 

 similarity to different bacteria, in consequence of which it is 

 impossible to obtain any certain information by means of an 

 ordinary microscopical examination ; the question to be 

 answered by the experiment is accordingly, whether these 

 small bodies are capable of multiplying. 



, FIG. 1. 

 Ranvier's Moist Chamber : a, seen in plan ; 5, in section. 



A drop of the liquid is transferred to the so-called " moist 

 chamber" as, for instance, Ranvier's (Fig. 1). This apparatus 

 is made by grinding a slight hollow in the middle of a common 

 object-glass ; around this hollow a groove is made of greater 

 depth to receive the water ; the drop of the nutritive solution, 

 which must be very small, is placed in the middle of the 

 hollow and covered with a cover-glass, which extends beyond 

 the groove ; when the cover-glass is in place, it is cemented 

 by means of vaseline, and the drop is thus spread out between 

 the cover-glass and the hollow of the object-glass, and is at the 

 same time protected by the water in the groove from 

 evaporating. 



