NOTES AND MEMORANDA. 461 



ten minutes to twenty-four hours. When withdrawn from this, they 

 have attached to them a piece of elder-pith, or are, if their size and 

 state permit of their heiug cut without any such aid, thrown at once 

 into alcohol ; the body now becomes surrounded with an elastic mass 

 of collodion, which solidifies without alteration of volume, and 

 encloses the pith if this has been already added. Thus treated, the 

 tissue is ready for immediate section, or may be kept in alcohol for 

 an indefinite period without danger. 



As the sections are made in the ordinary way, that is, the body 

 itself and the razor being both wetted with alcohol, it is obvious that 

 the collodion will be prevented from becoming dry ; there is no need 

 to remove the imbedding substance, and the section may be imme- 

 diately placed on a slide ; a drop of glycerine and a cover-glass are 

 then all that is necessary for the observer to find himself delighted 

 with an object, the optical properties of whose imbedding substance 

 are exactly the same as those of glass. Another advantage remains 

 to be noted, the collodion has not in M. Duval's sections lost its trans- 

 parency after a period of six months. 



A similar method may be used for foetal cerebral structures, and in 

 the study of the eye or of the cochlea and similar delicate parts. 



Method of Preserving the more delicate and perishable Animal 

 Tissues. — In a valuable article * on the development of the earth- 

 worm, Lumbriciis trapezoides Dugos, M. Kleinenberg says that whilst 

 a great part of the earliest formations of the egg can be made out in 

 the living state, the protoplasm being sufficiently transparent to 

 allow the internal parts to be seen, yet afterwards the precise outlines 

 of the cells disappear, and nothing can be seen but the grosser 

 structure. To make out the more delicate structure it is necessary 

 to employ reagents. 



Osmic acid applied in the state of vapour gives good results ; 

 but the preparations obtained by the use of a mixture of picric with 

 sulphuric acid are more satisfactory. It has, however, the same 

 drawback as osmic acid, of occasionally producing swellings in the 

 primitive blast(»mcres, which, if it only slightly alters the normal 

 conditions, renders the preparations less sightly. This difficulty is 

 overcome by the addition of a little kreosote. 



M. Kleinenberg, however, after many experiments, recommends 

 strongly the following method of preservation, which he used for the 

 particular researches treated of, and for the majority of other animal 

 tissues, especially for the more delicate and perishable. 



Prepare a saturated solution of picric acid in distilled water, 

 and to a hundred volumes of this add two volumes of concentrated 

 sulphuric acid ; all the picric acid which is precijDitated must be 

 removed by filtration. One volume of the liquid obtained in this 

 manner is to be diluted with three volumes of water, and, finally, as 

 much pure kreosote must be added as will mix. 



The object to be preserved should remain in this liquid for three, 

 four, or more hours ; then transferred, in order to harden it and 



* ' Quart. Jomn. Micr. Sci.,' xix. (1879) 206. 



