MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 7 



organisms, into the relations between their forms and external 

 influences and into all their biological functions. In the 

 former case all that is required is a culture 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 former kind may sometimes be of use in 

 affording information in the case mentioned above ; that of 

 a nutritive solution in which deposits of various kinds have 

 assumed a more or less deceptive resemblance to bacteria, in 

 consequence of which it is impossible to obtain any certain 

 information by means of an ordinary microscopical examination. 



FIG. 1. RANVIER'S Moist Chamber : a, plan ; 6, section. 



The question to be answered by the experiment is therefore, 

 whether these small bodies are capable of multiplying. 



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

 chamber, as, for instance, EANVIER'S (Fig. 1). This apparatus 

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

 object-glass ; round 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, while the water 

 in the groove makes it impossible for evaporation to take place. 



