14 THE CYTOLOGY AND LI FK-HISTO R Y OF BACTERIA 



/: THE MOUNTING OF MATERIAL 



(K, 9, 10, ir, 12, 22, 24, 29, 42, 53) 



Cytological preparations should be mounted upon the thinnest available 

 slides and coversHps, and it is a distinct advantage to prepare the smear upon 

 the CO verslip, so that the part of the preparation which is firmly adherent to 

 the glass is nearest to the objective of the microscope. It is also simpler to 

 transfer a coversHp from one reagent to another without the necessity oi 

 employing large volumes of fluid. The author has found sputum tubes and 

 watchglasses to be very suitable as containers, and the small volumes ot 

 reagents which they contain may be renewed at frequent intervals. 



Coverslips should be sealed to the slide, at the edges, with wax or vaseline, 

 unless the preparations are dehydrated and mounted, to which there is no 

 theoretical objection. In practice, however, it will be found that some 

 shrinkage and distortion will usually result, and the clarity ot the fniished 

 preparation will compare unfavourably with that of a simple water mount, 

 although possessing the advantage ot being permanent. It the edges are 

 carefully sealed a water mounted preparation will last for several days, in the 

 refrigerator, although it may deteriorate rapidly at room temperature. 



It is worth emphasising that far more detail can usually be made out in a 

 good photomicrograph, with all the advantages of colour filtration, than 

 can be discerned, by the most experienced observer, by direct microscopic 

 examination. Impcrmancncc ot preparations is thus ot little importance 

 provided that interesting appearances are photographed. It is also true that 

 appearances which cannot be reproduced, more or less at will, are unlikely 

 to be cither true or important, and their impermanencc is not to be regretted. 



Fig. 5 

 BASOPHILIC GRANULES IN THE CELL ENVELOPES OF BACILLUS 



(1,2) Partially acid-hydrolysed bacteria, stained with Giemsa, showing nuclear bodies and 

 granula and diffuse basophilia respectively in the cell envelopes. 



(3) Over-hydrolysed specimens showing occasional granules. 



(4, .5, 6) As (3) with added, extraneous DNA which has adhered in the form of stainable 

 granules, especially at the poles and cross-walls. This indicates that the granules appearing 

 naturally in (1) and (3) may well consist of similar nucleic acids translated from the nucleus 

 and cell envelopes by the hydrolysis procedure. Such granules have frequently been mis- 

 interpreted as nuclear bodies, mitotic centrioles, mitochondria, etc., etc. 



