ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 987 



Certes found tliis last action also with cyauiu or quinolein blue. 

 But in all these experiments the protoplasm, properly so called, 

 remains colourless, and the coloured solution always exercises an 

 injurious action on the vitality of the organisms ; so that it can only 

 be used in an extremely dilute condition and for a very short time. 



If, on the contrary, we try the converse method and place the 

 living organisms in a somewhat strong coloured solution they are 

 likely to die, either by exosmo?is or more often by actual poisoning. 

 It will therefore be useful to have a deeply coloured liquid which 

 is not poisonous, and which does not exercise any sensible osmotic 

 action on microscopic beings j^laced in it. To satisfy these con- 

 ditions it is sufficient to substitute for the coloured solutions water 

 holding in suspension coloured insoluble j^owder. Indian ink, on 

 account of its harmless nature and its deep colour, is very fit for this 

 purpose. It consists, as is well known, of lampblack and a gummy 

 substance, very slightly perfumed with musk or camphor. On 

 powdering it into water a very black liquid is obtained, owing to the 

 fine particles of carbon held in suspension ; it does not cause the 

 plasmolysis of the cells, and the organisms continue to live perfectly 

 in it. 



The process of using it is as follows : — A little Indian ink, not 

 too much perfumed, is rubbed up in a porcelain saucer. It ia 

 important to triturate it carefully. The liquid should show, under 

 the Microscope, excessively small granules of equal size, having a 

 lively Brownian movement ; it ought to have, when in very thin layers, 

 a dark grey, but not an opaque black tint. A drop of this liquid is 

 placed on a slide, the organisms to be examined are placed uj^on a 

 cover-glass, and this is applied to the drop. In this way black 

 particles between the cover-glass and the objects are avoided. 

 The objects appear remarkably illuminated on the grey-black 

 ground, so that their details can be seen distinctly. The car- 

 bonaceous matter does not seem to affect the organisms ; they bear 

 it very well, and the author has been able thus to preserve Spirogyra, 

 Vaucheria, Infusoria, &c., for several days alive. 



For prolonged observations it is of course advisable to use a moist 

 chamber, or to prevent evaporation by placing the preparation in an 

 atmosi)here saturated with aqueous vapour. 



Permanent preparations can also be made. To do this, the Indian 

 ink, in water, is gradually replaced under the cover-glass by Indian 

 ink in glycerin. Care must be taken that the black liquid does not 

 pass the edges of the cover, otherwise currents will be produced in 

 consequence of the evaporation, and the black particles will no 

 longer be uniformly distributed. 



Indian ink will, it seems to the author, render great service in 

 showing the gelatinous envelopes of the lower organisms, and the 

 gelatinized layers of the membranes of the higher plants. The 

 gelatinous envelopes of many filamentous alga>, of Glceocapsa, of the 

 colonics of zooglcea, &c., arc witli difficulty distinguishable in water, 

 but nothing, on the contrary, is so easy when the observation is made 

 in water charged with iudian ink. The method might probably also, 



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