PRESER VA TION. I 1 3 



Preservation of Infusoria. 



Up to within the last few years no attempts aiming at the preservation 

 of Infusoria in a condition approaching that which they exhibit in their 

 living state appear to have been successful. Ehrenberg and other early 

 investigators succeeded by careful desiccation in securing some shadowy 

 semblance of the pristine form of a few Ciliata, such as Paramecium and 

 Pleuronema, but for histologic purposes it is scarcely requisite to state 

 that types so preserved are practically worthless. Such progress has, 

 however, been made within the last half of the present decade in the 

 discovery of reagents and preservative fluids for the treatment of all organic 

 tissues, that the securing of permanent slides of the majority of infusorial 

 types is at the present day a mere matter of manipulation. That medium 

 which lays claim to the foremost position in the ranks for the conservation 

 of animalcules in their normal state, is undoubtedly osmic acid. Previously 

 utilized as an ordinary histologic reagent, it was first recommended to the 

 author by Professor Huxley in the year 1877 for the purpose now under 

 consideration, and is at the present time very generally employed. Applied 

 either in the form of vapour or as a solution in distilled water, having a 

 strength of from one to two per cent, the results obtained are most remark- 

 able. All structures, such as cilia, cirrhi and flagella, the internal endoplast, 

 and in Euglena and its allies the colours also, are preserved, the animal- 

 cules, excepting for the absence of motion, being scarcely distinguishable 

 from the living organisms. With certain of the more exceptionally 

 contractile forms, such as Stentor and Oxytricha, it is, as recommended 

 by M. A. Certes, better that the osmic acid should be employed in the 

 direct form by placing a drop of the solution on the covering glass before 

 laying the latter upon the slide containing the Infusoria ; this plan indeed 

 has been found by the author to be the most effectual and simple of appli- 

 cation in the majority of instances. For the Vorticellcs the employment 

 of a more concentrated solution of the acid than the one above mentioned 

 is recommended. As pointed out by M. Raphael Blanchard,* and also by 

 M. Certes, colouring reagents, such as haematoxylin, eosin, and picro- 

 carmine,t may be advantageously used in combination with osmic acid, 

 and assist greatly in developing the presence and form of the nucleus or 

 endoplast. The animalcules thus killed may be fastened down as per- 

 manent preparations, without the addition of any other preservative, and 

 afford valuable material for future reference and comparison. It will be 

 found that the smallest and most delicate flagelliferous species are equally 

 amenable to this course of treatment, preserving their flagella, and even, 

 in the case of the Choano-Flagellata, their delicate sarcode collars, in a 

 life-like form. As attested to in a succeeding chapter, the employment 



* ' Rev. Internal. Sci.,' iii. 1879. 



t In using this medium, the addition of one part of glycerine and one part of distilled water is 

 recommended by M. Certes. 



