ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 759 



from two to ten minutes in a concentrated solution of sulphate of 

 copper, then wash it quickly in distilled water, and submit it to the 

 action of a warm solution of potash. The cells inclosing saccharose 

 then show a pale blue colour, whilst those inclosing glucose assume 

 an orange-red tint. 



When the former are treated with warm sulphuric acid or nitrate of 

 potash, they lose their blue colour and become, like the latter, orange- 

 red. Gaston Bonnier,* by using Fehling's solution, has succeeded 

 in determining under the Microscope tlfe'localizatiim and the relative 

 abundance of the saccharoses and glucoses in the nectaries of flowers. 

 " A drop of Fehling's liquid, diluted, is put in the preparation, which 

 is then warmed. We observe under the Microscope in which part the 

 yellow or reddish-yellow precipitate is formed ; we then invert ; add 

 a drop of cupropotassic liquid, and warm again. The precipitate is 

 again examined. If it is much more abundant than at the first 

 examination it is because there is a considerable accumulation of 

 saccharose. There must be, of course, an excess of tartrate in the 

 first operation to cause the precipitation of the glucose." 



This method of working is very delicate, requiring great dexterity 

 and numerous precautions. If the liquid is boiled under the cover- 

 glass in such a way as to cause violent movements, the precipitate 

 gets distributed over the preparation ; which then assumes a general 

 tint of yellow, from which no conclusion can be drawn. The operation 

 must, moreover, be executed as quickly as possible, without which, 

 the water gradually dissolving the sugars, we should again have a 

 general precipitate. Finally the preparation must not be very thin 

 if we wish to form a correct judgment of the relative intensity of 

 the colours obtained by the reaction. The best conditions for ope- 

 rating are therefore with moderately thin sections. If the result 

 is too much obscured by the dissolving of the sugars in the water 

 of the Jpreparation, the sections must be warmed in a small tube 

 and taken up again with forceps to be examined as soon as the precipi- 

 tate is formed in the cells. As all these precautions were not taken 

 in the first attempts, this process of research appeared to be im- 

 practicable. Since then it has given very good results in many cases ; 

 for by comparing the observation of these more or less intense pre- 

 cipitates with the results given by the preceding process in well- 

 marked cases, I have found sufficient agreement. 



In fact, the yellow colour produced by Fehling's solution, and the 

 increase of the colour after inversion, are not absolute proofs of the 

 presence of glucoses and saccharoses ;| but it is an important character, 

 which, taken with others, may serve to demonstrate the presence of 

 sugars in the cells. If the real presence of the two kinds of sugar 

 has been recognized by testing, this process gives excellent indications 

 of the manner in which they are distributed in the tissues.!: 



Oils ; Oily matters ; Kesins. — The general reagent for these sub- 



* « Les Nectaires," Ann. Sci. Nat., 1879. 



t " As certain gums precipitate the tarfrate, tlie same takes place with certain 

 varieties of dextrine and ordinary dextrine in the presence of acids," 

 X G. Bonnier, loc. cit., p. 83. 



